Fix link to milestone page

Author: marcphilipp

documentation/src/docs/asciidoc/release-notes/release-notes-5.11.1.adoc

@@ -6,7 +6,7 @@
 *Scope:* Bug fixes and enhancements since 5.11.0
 
 For a complete list of all _closed_ issues and pull requests for this release, consult the
-link:{junit5-repo}+/milestone/79?closed=1+[5.11.1] milestone page in the JUnit repository
+link:{junit5-repo}+/milestone/80?closed=1+[5.11.1] milestone page in the JUnit repository
 on GitHub.