CI: check for maintainer comments

We don't want to accidentally introduce these again since we
deliberately switched all packages to maintainer variables. While this
probably could be made part of apkbuild-lint eventually, the Alpine TSC
hasn't yet made a decision about whether to switch to maintainer
variables or not to the best of my knowledge so I don't think it can be
made upstream policy yet. Make it a clear downstream policy via this
check for now as such.

Signed-off-by: Stefan Hansson <newbyte@postmarketos.org>
Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7824>

.ci/grep.sh

@@ -110,4 +110,11 @@ if grep -qr '/etc/modprobe.d' --exclude-dir='archived' \
 	exit_code=1
 fi
 
+# Disallow maintainer comments.
+if grep -qr '# Maintainer:' -- *; then
+	echo 'ERROR: Please use maintainer variables of the form maintainer="..." instead of maintainer comments of the form # Maintainer: ...'
+	grep --color=always -r '# Maintainer:' -- *
+	exit_code=1
+fi
+
 exit "$exit_code"