Change the if condition to trigger for pull request instead of main branch

Author: srinivasreddy

.github/workflows/reusable-change-detection.yml

@@ -132,7 +132,7 @@ jobs:
           echo "run-cifuzz=false" >> "$GITHUB_OUTPUT"
         fi
 
-        if [ "$GITHUB_BASE_REF" = "main" ]; then
+        if [ "$GITHUB_EVENT_NAME" == 'pull_request' ]; then
           CHANGED_FILES=$(git diff --name-only "origin/$GITHUB_BASE_REF..")
           # Check if changes are ONLY in configure/Makefile files
           if echo "$CHANGED_FILES" | grep -qE '^(configure.*|Makefile.*|.*\.m4)$' && \