add fetching git tags

[jannick0]

It would be helpful if git tags could be added after the check-out to have the relevant information available for composing the version string using the latest tag.

Putting git fetch --prune --unshallow into a step succeeded for one matrix job, failed for another matrix job. I believe this is due to competing processes accessing the repo to be checked out at the same time. This issue might have already been covered by actions/checkout I suspect, hence the idea above.

Many thanks.

[jannick0]

Setting fetch-depth: 0 fixes the issue.