Don't allow test-format.sh to be run locally

tests/test-format.sh

@@ -2,11 +2,13 @@
 
 set -e
 
-[ -z "$1" ] && exit
+if [ -z "$GITHUB_BASE_REF" ]
+then
+  echo "This script is only meant to be run in a GitHub Workflow"
+  exit 1
+fi
 
-basebranch=$1
-
-CHANGED_FILES=$(git diff --name-only "$basebranch"...HEAD)
+CHANGED_FILES=$(git diff --name-only "$GITHUB_BASE_REF"...HEAD)
 
 CHANGED=0