Skip the rebalance-sensitive consumer tests on 9.5

[delthas]

The ledger drain on rebalance and fromOffset consumer tests were written against librdkafka 2.12 and do not hold on the 2.3.0 that BB-806 pinned and that 9.5 keeps.

A controlled A/B on CI, 25 runs per arm over the full lib suite, isolates the cause — the first two arms differ only in package.json and yarn.lock:

tree	librdkafka	jobs failed
17 Jul (c16e5ddb)	2.3.0	10/25 = 40%
17 Jul (d7f3303d)	2.12.0	0/25
HEAD (52b9510f)	2.3.0	20/25 = 80%
HEAD + librdkafka 2.12	2.12.0	0/25
HEAD + this change	2.3.0	0/25

The librdkafka upgrade lands on 9.6 instead — S3C-11389 raises Federation's message-format pin, which removes the constraint that forced the downgrade in the first place. So this skips the two describes on 9.5 rather than touching the dependency.

Two things worth knowing for later:

• The skip cascades into 9.6, so the unskip has to land together with the upgrade there.
• The concurrency and rebalance describes are deliberately left enabled. They accounted for failures in 2 of the 25 pre-skip runs, so 9.5 may still see occasional flakiness from them.

Issue: BB-849

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.75%. Comparing base (52b9510) to head (fe1b973).

Additional details and impacted files

see 1 file with indirect coverage changes

Components	Coverage Δ
Bucket Notification	80.27% <ø> (ø)
Core Library	81.92% <ø> (-0.02%)	⬇️
Ingestion	70.09% <ø> (ø)
Lifecycle	80.46% <ø> (ø)
Oplog Populator	85.83% <ø> (ø)
Replication	62.01% <ø> (ø)
Bucket Scanner	85.76% <ø> (ø)

@@                 Coverage Diff                 @@
##           development/9.5    #2816      +/-   ##
===================================================
- Coverage            75.76%   75.75%   -0.01%     
===================================================
  Files                  200      200              
  Lines                13922    13922              
===================================================
- Hits                 10548    10547       -1     
- Misses                3364     3365       +1     
  Partials                10       10              

Flag	Coverage Δ
api:retry	9.10% <ø> (ø)
api:routes	8.87% <ø> (ø)
bucket-scanner	85.76% <ø> (ø)
ft_test:queuepopulator	10.98% <ø> (ø)
ingestion	12.26% <ø> (ø)
lib	8.81% <ø> (-0.02%)	⬇️
lifecycle	19.29% <ø> (-0.01%)	⬇️
notification	1.02% <ø> (ø)
oplogPopulator	0.13% <ø> (ø)
replication	18.84% <ø> (ø)
unit	54.88% <ø> (ø)

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[bert-e]

Waiting for approval

The following approvals are needed before I can proceed with the merge:

• the author

• 2 peers

[francoisferrand]

Let's not merge just yet, still trying to confirm the lib upgrade plan
(depending on it, maybe we can just revert in the 9.6 waterflow commit?)

[delthas]

Created the waterflow revert commit on w/9.6/bugfix/BB-849/skip-rebalance-sensitive-lib-tests

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