fix: force promote RPC hangs forever due to missing doAckCallback invocation

[bigsheeper]

What does this PR do?

Fixes a hang in the UpdateReplicateConfiguration RPC when force_promote=True is set.

Root Cause

In ack_callback_scheduler.go, triggerAckCallback handles force promote messages by launching a goroutine to call doForcePromoteFixIncompleteBroadcasts. The goroutine had its own defer g.Unlock() but never called doAckCallback.

doAckCallback is the only function that invokes MarkAckCallbackDone(), which closes the broadcast task's done channel. broadcastScheduler.AddTask calls task.BlockUntilDone() on this channel, so without doAckCallback being called, BlockUntilDone() blocks forever — leaving the force promote RPC permanently hung.

Fix

Chain doAckCallback(task, g) after doForcePromoteFixIncompleteBroadcasts(task) in the same goroutine. doAckCallback already handles g.Unlock() via its internal defer, so the separate unlock defer in the goroutine is also removed.

// Before (buggy):
go func() {
    defer func() {
        s.rkLockerMu.Lock()
        g.Unlock()
        s.rkLockerMu.Unlock()
    }()
    s.doForcePromoteFixIncompleteBroadcasts(task)
}()

// After (fixed):
go func() {
    s.doForcePromoteFixIncompleteBroadcasts(task)
    s.doAckCallback(task, g)  // closes done channel, unblocks BlockUntilDone()
}()

Tests

Verified with E2E tests covering the full force promote lifecycle:

• Force promote on primary cluster rejected
• Force promote with non-empty clusters/topology rejected
• Force promote succeeds on secondary with data integrity (1000 rows replicated + 500 new rows post-promote)
• Force promote on already-promoted cluster rejected

issue: #47352

[sre-ci-robot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.98%. Comparing base (8c8062f) to head (e595e25).
⚠️ Report is 19 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #48535       +/-   ##
===========================================
+ Coverage   74.87%   83.98%    +9.11%     
===========================================
  Files        1484      627      -857     
  Lines      246812   103896   -142916     
===========================================
- Hits       184797    87259    -97538     
+ Misses      53665    16637    -37028     
+ Partials     8350        0     -8350     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	83.98% <ø> (∅)
Go	∅ <ø> (∅)
see 2111 files with indirect coverage changes

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[zhikunyao]

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