fix(extensions): underscores are invalid in prerelease

[roxspring]

When using GitHub Actions & Dependabot I've been hitting the following:

1: Task failed with an exception.
-----------
* What went wrong:
A problem occurred configuring root project 'root-project'.
> io.github.z4kn4fein.semver.VersionFormatException: Pre-release part 'dependabot-github_actions-softprops-action-gh-release-2' contains an invalid character. (dependabot-github_actions-softprops-action-gh-release-2.1)
gradle/actions: Writing build results to /home/runner/work/_temp/.gradle-actions/build-results/__run-1758664924990.json

IIUC this boils down to an _ being contributed to the prerelease label which clearly is not a valid character.

This PR includes a test demonstrating the problem, a fix, and a required commit to update the copyright headers 🤷

[tbcrawford]

Hi there! Thank you so much for your contribution and fixing this bug! I just have one tiny ask and I'd be happy to run this through and get a release cut soon. Actually, it looks like I was able to easily make this change. Let me get this run through here and get a new release out!

Looks like there is an issue with cross user branches. I will have to look at this later when I have more time.

[tbcrawford]

Could you rename this to invalidSemverCharacters? Reading back over this didn't make much sense to me why we would be trying to replace all "valid characters" with - 😅

Suggested change

	private val validCharacters: Regex = """[^0-9A-Za-z\-.]+""".toRegex()
	private val invalidSemverCharacters: Regex = """[^0-9A-Za-z\-.]+""".toRegex()

[roxspring]

Yeah, I also spent too long trying to figure out whether that was a list of the valid vs invalid characters. Renaming the val should make that a little clearer.

[roxspring]

Actually... validCharacters is referenced again a few lines down which will also need updating to invalidSemverCharacters.

[tbcrawford]

Good call! I overlooked that. Thanks!

[tbcrawford]

@roxspring I ended up having to bring this branch (relevant PR) into the repository itself since I'm having issues with cross-repo pull requests at the moment. I have to look into that issue. You can find this fix published in 2.0.4. Thank you again for your contributions!