code-server: Depends on libsecret and pkg-config for Linux

libsecret is not spelled out explicitly in the dependencies, but
it's mentioned as a step here: coder/code-server#735 (comment)

pkg-config was found as a required dep by CI

Author: rwhogg

Formula/code-server.rb

@@ -15,6 +15,11 @@ class CodeServer < Formula
   depends_on "yarn" => :build
   depends_on "node"
 
+  unless OS.mac?
+    depends_on "pkg-config" => :build
+    depends_on "libsecret"
+  end
+
   def install
     system "yarn", "--production"
     libexec.install Dir["*"]