precheck: fix false warning about content-divergence creation
Before this patch, if we try to `hg prune` (without any successors) an
already obsoleted cset which has at least one successor, it would false
warn about new content-divergence. As we know, pruning cset without any
successors can not create any divergence.
Differential Revision: https://phab.mercurial-scm.org/D12002
#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