While `fixup! ` is fine, `squash! ` means that the commit message needs
tweaking, which cannot be done automatically during merging (i.e. it
should be done by the PR author).
Previously, `validate-commit-message` would always allow
`squash! `-prefixed commits, which would cause problems during merging.
This commit changes `validate-commit-message` to make it configurable
whether such commits are allowed and configures the
`gulp validate-commit-message` task, which is run as part of the `lint`
job on CI, to not allow them.
NOTE: This new check is disabled in the pre-commit git hook that is used
to validate commit messages, because these commits might still be
useful during development.
PR Close#32023
c0d5684078