test(actions): Using git diff to check updated cls.

Author: fky2015

Diff for: .github/workflows/test.yaml

@@ -27,3 +27,14 @@ jobs:
       - uses: actions/checkout@v2
       - name: Check spelling of bithesis.dtx
         uses: crate-ci/typos@master
+
+  ensure_updated_cls:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: xu-cheng/texlive-action/full@v1
+        with:
+          run: |
+            apk add make
+            make copy
+            [[ `git status --porcelain`]]