missing dollar sign in check script for hyperlinks? (#780)

Signed-off-by: Chun Tao <[email protected]>

Author: ctao456

.github/workflows/pr-dockerfile-path-scan.yaml

@@ -178,7 +178,7 @@ jobs:
           fail="FALSE"
           merged_commit=$(git log -1 --format='%H')
           changed_files="$(git diff --name-status --diff-filter=ARM ${{ github.event.pull_request.base.sha }} ${merged_commit} | awk '/\.md$/ {print $NF}')"
-          if  [ -n "changed_files" ]; then
+          if  [ -n "$changed_files" ]; then
             for changed_file in $changed_files; do
               echo $changed_file
               url_lines=$(grep -H -Eo '\]\(http[s]?://[^)]+\)' "$changed_file" | grep -Ev 'GenAIComps/blob/main')