[doc] linkspector should check only changed documentation lines

Unfortunately this change will prevent us from discovering broken links in files which have a reference to the affected ones.
However, checking too many links causes sometimes "Too Many Requests" error, so we would be getting some false positives.

Author: knopers8

.github/workflows/linkspector.yml

@@ -12,4 +12,4 @@ jobs:
           github_token: ${{ secrets.github_token }}
           reporter: github-pr-check
           fail_level: any
-          filter_mode: nofilter
+          filter_mode: added