Use better names in CI and put checkgenerate into separate step

[timostamm]

This renames workflows and jobs for better readability:

 

Other changes:

• "Check generate" moves to a separate job to for faster feedback.
• We drop step names because most steps already have self-explanatory names.
• I couldn't see any reason why we check out with fetch-depth: 2, so this drops the setting to rely on the default.

Looks like branch protection rules need an update - I'll sort this out after review.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Mar 11, 2026, 6:23 PM

[stefanvanburen]

I realize that this is the existing behavior, but it feels somewhat weird to get the latest buf binary from (presumably?) buf-action with setup_only and sidestep the pinned buf in the Makefile, but probably fine in the sense that it shouldn't change generation/formatting anyway.