docs: manually bump pre-commit refs (#10814)

## Summary

rooster should pick those up, but those 2 references were added to 0.5.8
while a 0.5.9 was already released
(https://github.com/astral-sh/uv/commit/f5add0ca5e2711396e033741375049d0454730f4),
so they never got bumped automatically.

I've searched for other cases like this in the documentation on other
versions, just in case, and it seems that this is the only case.

docs/guides/integration/pre-commit.md

@@ -16,7 +16,7 @@ pre-commit, add the following to the `.pre-commit-config.yaml`:
 ```yaml title=".pre-commit-config.yaml"
 - repo: https://github.com/astral-sh/uv-pre-commit
   # uv version.
-  rev: 0.5.8
+  rev: 0.5.21
   hooks:
     - id: uv-lock
 ```
@@ -26,7 +26,7 @@ To keep your `requirements.txt` file updated using pre-commit:
 ```yaml title=".pre-commit-config.yaml"
 - repo: https://github.com/astral-sh/uv-pre-commit
   # uv version.
-  rev: 0.5.8
+  rev: 0.5.21
   hooks:
     - id: uv-export
 ```