ensure latest tag is used to determine versions

[jameslamb]

Contributes to https://github.com/rapidsai/github-infrastructure/issues/63

Mistakes in forward-mergers can sometimes lead to a weird mix of tags in git history, which can trip up logic that relies on those tags to compute things like versions for image URIs.

git describe --tags --first-parent ensures we get the expected behavior (version = tag "closest" to HEAD) even when mistakes are made in the forward-merger process.

See rapidsai/docker#867 and https://github.com/rapidsai/github-infrastructure/issues/63 for much more detail.

Notes for Reviewers

How I tested this

These commands are equivalent on main here.

$ git checkout main
$ git fetch upstream --tags
$ git describe --abbrev=0 --tags
v26.06.00a

$ git describe --abbrev=0 --tags --first-parent
v26.06.00a

Just doing this preventatively.

[gforsyth]

Big fan of preventative measure.