ci: catch new untracked files after running tests

.github/workflows/push.yml

@@ -152,10 +152,15 @@ jobs:
           if-no-files-found: warn
           retention-days: 7
 
-      - name: Check out.test.toml files are up to date
+      - name: Check no files changed or appeared after running tests
         run: |
+          # Register untracked files with intent-to-add so `git diff` reports them
+          # too; a plain `git diff` ignores new files, which is how a missing
+          # out.test.toml previously slipped through. Ignored test artifacts are
+          # unaffected because intent-to-add respects .gitignore.
+          git add --intent-to-add .
           if ! git diff --exit-code; then
-            echo "ERROR: detected changed files in the repository; Most likely you have out.test.toml files that are out of date. Run 'go test ./acceptance -run \"^TestAccept$\" -only-out-test-toml' to update."
+            echo "ERROR: detected changed or new files in the repository; Most likely you have out.test.toml files that are out of date. Run 'go test ./acceptance -run \"^TestAccept$\" -only-out-test-toml' to update."
             exit 1
           fi