change the check for publishing

[devoncarew]

We should not look for changed files when publishing; the user is indicating that they want a publish. The checks should be:

• the tag is well formed (vX.X.X or name_vX.X.X)
• if a monorepo, the package exists
• the tag version matches the changelog verson
• the tag version matches the pubspec version

[devoncarew]

We want to avoid this:

Run dart pub global run firehose --publish
Repository changed files:

Repository publishable packages:
  package:simple_lint_rules, 2.0.1, .

Found 0 changed package(s).

[devoncarew]

We can use git.refName for this.