Ensure version is valid before passing it to semver

[ygrishajev]

There is a use case when using a custom tagPrefix.
In my monorepo I'm trying to implement semver prerelease flow with a custom prefix like so:

<app>/v<semver>-alfa.0 -> <app>/v<semver>-alfa.1 -> <app>/v<semver>-beta.0 -> <app>/v<semver>

It works fine till first stable version is created. After this new pre-release ones are failing as tags are technically invalid according to semver.

This PR attempts to address this issue.

I'd be happy to discard it if there is an existing way to address this.

[webpro]

After this new pre-release ones are failing as tags are technically invalid according to semver.

Although tags don't require semver validness, allowing this in a plugin might cause all sorts of issues, also in release-it core. Didn't investigate all the way through, but tbh doesn't come across as a great idea initially.