Fix typo in GitLab integration docs (astral-sh#9047)

## Summary
This PR changes the mentioned file name `requirement.txt` to
`requirements.txt` (add "s") to be consistent.

docs/guides/integration/gitlab.md

@@ -66,5 +66,5 @@ variables:
 
 To opt-out again, the `--no-system` flag can be used in any uv invocation.
 
-When persisting the cache, you may want to use `requirement.txt` or `pyproject.toml` as
+When persisting the cache, you may want to use `requirements.txt` or `pyproject.toml` as
 your cache key files instead of `uv.lock`.