[fix] [test] fix test code create namespace conflict

[thetumbled]

Motivation

Running test code org.apache.pulsar.broker.transaction.TransactionTest, exceptions will be throw as:

org.apache.pulsar.client.admin.PulsarAdminException$ConflictException: Namespace already exists

	at org.apache.pulsar.client.admin.PulsarAdminException.wrap(PulsarAdminException.java:252)
	at org.apache.pulsar.client.admin.internal.BaseResource.sync(BaseResource.java:352)
	at org.apache.pulsar.client.admin.internal.NamespacesImpl.createNamespace(NamespacesImpl.java:211)
	at org.apache.pulsar.broker.transaction.TransactionTest.testReadCommittedWithCompaction(TransactionTest.java:1858)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

This is because the previous test code has created the same namespace.

Modifications

Using a different namespace to avoid confliction.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: thetumbled#35

[thetumbled]

/pulsarbot rerun-failure-checks

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.62%. Comparing base (153cd5e) to head (7b4e2f8).
⚠️ Report is 1609 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #21941      +/-   ##
============================================
+ Coverage     73.53%   73.62%   +0.09%     
+ Complexity    32433    32427       -6     
============================================
  Files          1861     1861              
  Lines        138675   138673       -2     
  Branches      15184    15182       -2     
============================================
+ Hits         101974   102099     +125     
+ Misses        28840    28677     -163     
- Partials       7861     7897      +36     

Flag	Coverage Δ
inttests	24.07% <ø> (?)
systests	23.66% <ø> (-0.12%)	⬇️
unittests	72.91% <ø> (+<0.01%)	⬆️

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see 94 files with indirect coverage changes

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