fix(gatsby-plugin-netlify): add warning instead for invalid he… (#18326)

* fix(gatsby-plugin-netlify): add warning instead of breaking when invalid header

* converted to more jest like approach

* fix review

Author: wardpeet

packages/gatsby-plugin-netlify/src/__tests__/__snapshots__/build-headers-program.js.snap

@@ -1,13 +1,15 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`with caching headers 1`] = `
+exports[`build-headers-program with badly headers configuration 1`] = `
 "## Created with gatsby-plugin-netlify
 
 /*
   X-Frame-Options: DENY
   X-XSS-Protection: 1; mode=block
   X-Content-Type-Options: nosniff
   Referrer-Policy: same-origin
+X-Frame-Options
+  sameorigin
 /component---node-modules-gatsby-plugin-offline-app-shell-js-78f9e4dea04737fa062d.js
   Cache-Control: public, max-age=31536000, immutable
 /0-0180cd94ef2497ac7db8.js
@@ -76,7 +78,83 @@ exports[`with caching headers 1`] = `
 "
 `;
 
-exports[`with security headers 1`] = `
+exports[`build-headers-program with caching headers 1`] = `
+"## Created with gatsby-plugin-netlify
+
+/*
+  X-Frame-Options: DENY
+  X-XSS-Protection: 1; mode=block
+  X-Content-Type-Options: nosniff
+  Referrer-Policy: same-origin
+/component---node-modules-gatsby-plugin-offline-app-shell-js-78f9e4dea04737fa062d.js
+  Cache-Control: public, max-age=31536000, immutable
+/0-0180cd94ef2497ac7db8.js
+  Cache-Control: public, max-age=31536000, immutable
+/component---src-templates-blog-post-js-517987eae96e75cddbe7.js
+  Cache-Control: public, max-age=31536000, immutable
+/component---src-pages-404-js-53e6c51a5a7e73090f50.js
+  Cache-Control: public, max-age=31536000, immutable
+/component---src-pages-index-js-0bdd01c77ee09ef0224c.js
+  Cache-Control: public, max-age=31536000, immutable
+/pages-manifest-ab11f09e0ca7ecd3b43e.js
+  Cache-Control: public, max-age=31536000, immutable
+/webpack-runtime-acaa8994f1f704475e21.js
+  Cache-Control: public, max-age=31536000, immutable
+/styles.1025963f4f2ec7abbad4.css
+  Cache-Control: public, max-age=31536000, immutable
+/styles-565f081c8374bbda155f.js
+  Cache-Control: public, max-age=31536000, immutable
+/app-f33c13590352da20930f.js
+  Cache-Control: public, max-age=31536000, immutable
+/static/*
+  Cache-Control: public, max-age=31536000, immutable
+/sw.js
+  Cache-Control: no-cache
+/offline-plugin-app-shell-fallback/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </component---node-modules-gatsby-plugin-offline-app-shell-js-78f9e4dea04737fa062d.js>; rel=preload; as=script
+/hi-folks/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-templates-blog-post-js-517987eae96e75cddbe7.js>; rel=preload; as=script
+/my-second-post/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-templates-blog-post-js-517987eae96e75cddbe7.js>; rel=preload; as=script
+/hello-world/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-templates-blog-post-js-517987eae96e75cddbe7.js>; rel=preload; as=script
+/404/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-pages-404-js-53e6c51a5a7e73090f50.js>; rel=preload; as=script
+/
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-pages-index-js-0bdd01c77ee09ef0224c.js>; rel=preload; as=script
+/404.html
+  Link: </webpack-runtime-acaa8994f1f704475e21.js>; rel=preload; as=script
+  Link: </styles-565f081c8374bbda155f.js>; rel=preload; as=script
+  Link: </app-f33c13590352da20930f.js>; rel=preload; as=script
+  Link: </0-0180cd94ef2497ac7db8.js>; rel=preload; as=script
+  Link: </component---src-pages-404-js-53e6c51a5a7e73090f50.js>; rel=preload; as=script
+"
+`;
+
+exports[`build-headers-program with security headers 1`] = `
 "## Created with gatsby-plugin-netlify
 
 /*
@@ -155,7 +233,7 @@ exports[`with security headers 1`] = `
 "
 `;
 
-exports[`without caching headers 1`] = `
+exports[`build-headers-program without caching headers 1`] = `
 "## Created with gatsby-plugin-netlify
 
 /*