ci: Make stack build fail when lock file is out of date

When updating stack.yaml, we need to make sure to update stack.yaml.lock, too.

This check prevents them from getting out of sync by failing CI in this case.

This improves cachability.

.github/workflows/ci.yaml

@@ -222,7 +222,7 @@ jobs:
         if: ${{ matrix.deps }}
         run: ${{ matrix.deps }}
       - name: Build with Stack
-        run: stack build --local-bin-path result --copy-bins
+        run: stack build --lock-file error-on-write --local-bin-path result --copy-bins
       - name: Strip Executable
         run: strip result/postgrest*
       - name: Save built executable as artifact