update git pre-push hook to check for uncommitted changes

[Gladdstone]

Resolves #149599

Please let me know if there are any phrasing issues.

[rustbot]

r? @Mark-Simulacrum

rustbot has assigned @Mark-Simulacrum.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[jyn514]

please don’t do this. run on the staged changes in a temporary directory instead: #125654

[jyn514]

there’s some prior art in #147084 you could look at.

cc @Kobzol