[GitHub Actions] Show diff if test vectors generated by CI do not match.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

.github/workflows/test_vectors.yml

@@ -34,4 +34,4 @@ jobs:
         run: ./regenerate.sh ${{ matrix.kind }} ${{ matrix.extension }}
 
       - name: Verify there are no changes
-        run: test -z "$(git status --porcelain)"
+        run: git diff; git ls-files --others --exclude-standard; test -z "$(git status --porcelain)"