Exclude uv.lock from the CI working-tree guard

`uv sync --no-sources` rewrites uv.lock in place (swaps the local editable
langchain-core/-tests source for the PyPI registry), so the post-test
`git diff --exit-code` guard saw an expected diff and failed. Scope the
guard to ignore uv.lock; it still catches stray files written by a test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: shixish

.github/workflows/ci.yml

@@ -54,4 +54,7 @@ jobs:
       - run: uv sync --no-sources --group test
       - run: make test
       - name: Check for unexpected file changes
-        run: git diff --exit-code
+        # `uv sync --no-sources` rewrites uv.lock in place (local editable
+        # source -> PyPI registry); that diff is expected in CI. Exclude it so
+        # the guard still catches stray files a test might have written.
+        run: git diff --exit-code -- ':!uv.lock'