CI+Meta: Add Signed-off-by tag filter to the commit message linter

Author: https://github.com/IdanHo
Commit: https://github.com/SerenityOS/serenity/commit/24ed8511dd8
Pull-request: https://github.com/SerenityOS/serenity/pull/9880

.github/workflows/lintcommits.yml

@@ -55,6 +55,14 @@ jobs:
           pattern: '^.+[^.\n](\n.*)*$'
           error: 'Commit title ends in a period'
 
+      - name: Check body for sign off
+        if: ${{ success() || failure() }}
+        uses: tim-actions/commit-message-checker-with-regex@v0.3.1
+        with:
+          commits: ${{ steps.get-pr-commits.outputs.commits }}
+          pattern: '^((?!Signed-off-by: )[\s\S])*$'
+          error: 'Commit body contains a Signed-off-by tag'
+
       - name: Comment on PR
         if: ${{ failure() && !github.event.pull_request.draft }}
         uses: IdanHo/comment-on-pr@5f51df338210754f519f721f8320d8f72525a4d0

Meta/lint-commit.sh

@@ -46,5 +46,10 @@ while read -r line; do
   if [[ $line_length -gt 72 ]] && (echo "$line" | grep -P -v -q "$url_pattern"); then
     error "Commit message lines are too long (maximum allowed is 72 characters)"
   fi
+
+  if [[ "$line" == "Signed-off-by: "* ]]; then
+    error "Commit body contains a Signed-off-by tag"
+  fi
+
 done <"$commit_file"
 exit 0