proper diff and fetch main

Author: jazzsequence

.github/workflows/prettier.yml

@@ -32,7 +32,8 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
-          CHANGED_FILES=$(git diff --name-only $BASE_BRANCH | grep -E '\.js$|\.jsx$|\.ts$|\.tsx$' || echo "")
+          git fetch origin main
+          CHANGED_FILES=$(git diff --name-only origin/main...HEAD | grep -E '\.js$|\.jsx$|\.ts$|\.tsx$' || echo "")
           if [ -n "$CHANGED_FILES" ]; then
             echo "Fixing the following files:"
             echo "$CHANGED_FILES"