ci: add check for symlinks

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1169>

.gitlab-ci.yml

@@ -417,6 +417,7 @@ check commits:
     - when: 'always'
   script:
     - ci-fairy check-commits --textwidth 0 --no-signed-off-by
+    - ci/check-for-symlinks.sh
 
 clippy:
   extends: .img-stable

ci/check-for-symlinks.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+LINKS=`find -type l`
+if test -z $LINKS; then
+  echo "No symlinks found."
+else
+  echo "===> FOUND SYMLINKS!"
+  echo
+  echo "$LINKS"
+  echo
+  echo "Please replace these with actual files."
+  exit 1;
+fi