Bump gitlab-shell to 14.57.3

What does this MR do and why?

Bumps GITLAB_SHELL_VERSION from 14.57.2 to 14.57.3, shipping the Cells SSH routing fix from gitlab-shell!1546 (merged).

What the fix does

The Cells pull path kept the proxied HTTP request body open until the SSH session ended, even though pull negotiation finishes before the pack transfer. The body then sat idle for the whole transfer, so an intermediary's idle client-body timeout killed proxied clones after about 60 seconds. The body is now closed once negotiation completes, and a flush-pkt is injected so protocol v2 clients keep working.

This is the Cells port of the Geo fix (gitlab-shell!1537 (merged)) that shipped in 14.57.2. That change only touched the Geo PullCommand, so the Cells path was still affected.

Push deliberately continues to stream its raw request body, because a push body carries the pack data.

Why this is needed

This unblocks re-enabling the Topology Service client for gitlab-shell on GitLab.com staging (gitlab-shell#864 (closed)). Two earlier enablement attempts were reverted after routed ssh-upload-pack requests failed with PROTOCOL_ERROR, the first at ~64s, matching the timeout this fix addresses. GitLab.com builds gitlab-shell from the pinned GITLAB_SHELL_VERSION rather than main, so this bump is required for the fix to reach staging.

Release contents

v14.57.3:

• Cells: Close Cells pull request body after negotiation !1546 (merged)
• Deduplicate Gitaly integration test setup !1544 (merged)
• Deduplicate LFS transfer test setup !1542 (merged)

The latter two are test-only refactors.

Verification

Confirmed the published tag contains the fix:

git merge-base --is-ancestor 7f82d3a9 v14.57.3   ->  true
v14.57.3:VERSION                                 ->  14.57.3
v14.57.3 cells.go                                ->  pipeRequest(ctx, c.ReadWriter, readUploadPackRequest, gitClient.SSHUploadPack)

References

• gitlab-shell!1546 (merged) - the fix
• gitlab-shell!1547 (merged) - Release v14.57.3
• gitlab-shell!1537 (merged) - Geo precedent
• gitlab-shell#864 (closed) - Cells: Validate SSH routing for Git pull and push on staging

MR acceptance checklist

• Version bump only; no application code changes.
• Target version is a published, verified gitlab-shell tag.