branchcache: cleanup the final key generation after update
A lot of duplicated work seemed to be done, as we already update the tiprev and
tipnode when needed right before. So we simplify that part to focus on the
filtered hash.
See inline comment for details.
#require cargo test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/../rust
Check if Cargo.lock is up-to-date. Will fail with a 101 error code if not.
$ cargo check --locked --all --quiet
However most CIs will run `cargo build` or similar before running the tests, so we need to check if it was modified
$ testrepohg diff Cargo.lock