[v3-2-test] Breeze: fail fast when building provider sdists from a git worktree (#65771)

[github-actions]

• Breeze: fail fast when building provider sdists from a git worktree

flit's --use-vcs silently produces incomplete sdists when run from a
git worktree add ... directory, because flit.vcs.identify_vcs() checks
(p / ".git").is_dir() and in a worktree .git is a file (gitdir:
pointer). flit then falls back to a minimal sdist that omits docs/,
tests/, provider.yaml and other tracked files, and the resulting
packages fail reproducibility checks against released sdists on
dist.apache.org — with no warning.

breeze release-management prepare-provider-distributions now exits 1
with a clear explanation and a workaround (use a plain checkout, or
pass --distribution-format wheel — wheels are unaffected) when it
detects it is running from a worktree and would build sdists.

Wheels and providers using hatchling with explicit sdist includes are
not affected, so only sdist and both formats trigger the check.

• Breeze: detect Docker-mounted worktrees in provider-sdist check

When Breeze runs prepare-provider-distributions from a git worktree, the worktree's .git file carries an absolute gitdir: pointer to the main repo's .git/worktrees/ directory. Only the worktree folder is bind-mounted into Breeze's Docker container, so that pointer target is unreachable from inside the build. flit's VCS detection then either fails or silently produces an incomplete sdist.

Expand check_flit_worktree_compatibility to parse .git and branch on the failure mode: read error, unexpected format, missing gitdir target (Docker mount case), or healthy host-side worktree. Tests cover all paths.

• Link upstream flit issue/PR + tracking issue at the workaround site

Add references to pypa/flit#798 and pypa/flit#799 in the docstring of check_flit_worktree_compatibility, and the Airflow tracking issue #65772 at both the helper and its call site. CLAUDE.md requires the tracking-issue URL to appear at the workaround site in the code so the follow-up work is discoverable from any grep or code review.
(cherry picked from commit ddf3c7a)

Co-authored-by: Jarek Potiuk jarek@potiuk.com