Use the correct path to the patch file.

Author: desrosj

.github/workflows/test-and-zip-default-themes.yml

@@ -172,7 +172,7 @@ jobs:
         if: ${{ steps.built-file-check.outputs.uncommitted_changes == 'true' }}
         with:
           name: pr-built-file-changes
-          path: changes.diff
+          path: src/wp-content/themes/${{ matrix.theme }}/changes.diff
 
       - name: Ensure version-controlled files are not modified or deleted
         run: git diff --exit-code