Don't run writeVersionLocks when checking out a new branch

[jackwickham]

What happened?

When checking out a branch (using the terminal) which changes versions.props and versions.locks, the plugin triggers writeVersionLocks to run redundantly.

What did you want to happen?

It should not have needed to run it. Ideally it would notice that versions.lock also got updated at the same time, so there's no need to rerun it.