convert pre-release to release on VCMI release

[kambala-decapitator]

I suggest the following workflow when a VCMI release is published:

1. find the pre-release that was used to create VCMI release (as it may not necessarily be the latest one)
2. rename the pre-release from <date> to x.y.z (<date>)
3. convert it to the latest release
4. change attached tag to x.y.z (it won't delete existing tag)

This way it'd be clear which dependencies to use for a given release.

Point 1 should be done in a VCMI repo workflow and then notify this repo of release passing the pre-release name, we already have such process for our Homebrew repo: https://github.com/vcmi/vcmi/blob/develop/.github/workflows/on-release.yml