chore: Making the regex to catch cli reference strict by adding word boundary anchor

Right now the regex is over-matching and is returning true for references like these:
from ..utils._client_labels_utils import EVAL_CLIENT_LABEL

Co-authored-by: Ankur Sharma <ankusharma@google.com>
PiperOrigin-RevId: 857255767

Author: ankursharmas

.github/workflows/check-file-contents.yml

@@ -96,7 +96,7 @@ jobs:
             echo ""
 
             set +e
-            FILES_WITH_FORBIDDEN_IMPORT=$(grep -lE '^from.*cli.*import.*$' $CHANGED_FILES)
+            FILES_WITH_FORBIDDEN_IMPORT=$(grep -lE '^from.*\bcli\b.*import.*$' $CHANGED_FILES)
             GREP_EXIT_CODE=$?
             set -e