Release automation does not kick off if package is bumped but not root version (or vice versa)

If an engineer creates a release PR that bumps the version of one or more packages but does not bump the root version, and then they merge the PR, the release automation will not kick off. This causes confusion, and they reach out to us for help. (Although less likely, the same thing would happen if the root version is bumped but no packages are bumped).

We need to prevent such PRs from being merged.

Start by tracing the release automation and its version checks for the root package and individual packages. Add validation that prevents merging when only one side is bumped, then verify that matching root and package version changes still allow the release automation to run.

Written by the indexing model from the issue text.