tests: split up test-rebase-obsolete.t in four pieces
The test case took 42 seconds to run the test before this patch and 12
seconds after (wall time, of course).
Differential Revision: https://phab.mercurial-scm.org/D10255
#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