ci: Improve release notes processing

Makes the perl regex stop at the first "\nChanges in" hit, instead of
"\n\n". This should allow us to use more freely formatted notes in the
release.

.github/workflows/release.yml

@@ -69,7 +69,7 @@ jobs:
           # Extract the changelog
           {
             echo "releaseChangelog<<EOF"
-            perl -0777nE 'print $& if /(?<=\n\n).*?(?=\n\n)/sg' NEWS
+            perl -0777nE 'print $& if /(?<=\n\n).*?(?=\nChanges in)/sg' NEWS
             echo "\nEOF"
           } | tee -a $GITHUB_ENV
           echo $releaseChangelog