ci: enforce README sync in CI test job

Add a `README up to date` step after `make test` that runs
`git diff --exit-code -- README.md` so CI fails when query
changes update README.md but the docs change is not
committed.

Author: lewis6991

.github/workflows/ci.yml

@@ -107,6 +107,9 @@ jobs:
       - name: Run Test
         run: make test
 
+      - name: README up to date
+        run: git diff --exit-code -- README.md
+
       - name: Download tsqueryls
         run: make tsqueryls