[fix][test] fix flaky testNegativeAcksWithBackoff when batch enabled.

[thetumbled]

Main Issue: #23885

Motivation

When batch message is negative ack, some undetermined behavior may occur. For example,

• There are 10 messages batched into one message, all of them are unbatch into consumer's receiver queue.
• consumer negative ack the first 5 messages.
• before the consumer negative ack another 5 messages, the negatve ack tracker trigger the redelivery request.
• broker dispatch this batched message to consumer.
• consumer clear the remaining 5 messages in the queue, and refill 10 messages into the queue.
• Message duplication issue occurs.
  IMO, suck kind of problem is reasonable as we only provide At-Least-Once semantices.

Modifications

This unit test don't handle the batch case at some time.
Negative ack one message is enough for this test in batch case.

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Documentation

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.24%. Comparing base (bbc6224) to head (4ab5cc3).
Report is 917 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23986      +/-   ##
============================================
+ Coverage     73.57%   74.24%   +0.66%     
+ Complexity    32624    32265     -359     
============================================
  Files          1877     1853      -24     
  Lines        139502   143847    +4345     
  Branches      15299    16339    +1040     
============================================
+ Hits         102638   106793    +4155     
+ Misses        28908    28648     -260     
- Partials       7956     8406     +450     

Flag	Coverage Δ
inttests	26.76% <ø> (+2.18%)	⬆️
systests	23.23% <ø> (-1.09%)	⬇️
unittests	73.76% <ø> (+0.91%)	⬆️

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