fix(version): fix vim.version().prerelease

[bfredl]

fixes #28782 (when backported)

[wookayin]

Thought not mandatory, would it be possible to detect whether CI is building a "release" and check prerelease in version_spec so that #28782 can be prevented in the future?

[bfredl]

well, the release flow just doesn't run any tests at all.

[dundargoc]

It might be possible to apply different git tags to the repo and test expected version output, that way it won't matter if a commit was "release or not".

So basically in a test run "git tag 1.0" and then check stuff works on release tags. Unsure if it's worth it tho.

[github-actions]

Successfully created backport PR for release-0.10:

• fix(version): fix vim.version().prerelease #28787