Fix DrainBacklogNoPollersIsolationGroup tests

[Shaddoll]

What changed?
Fix DrainBacklogNoPollersIsolationGroup tests

Why?
The tests are flaky because we're not using the same timeSource across different components, and this makes some tasks expire and the tests never end.

How did you test it?
existing tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 68.22%. Comparing base (c6a145d) to head (8efefd1).

Additional details and impacted files

Files	Coverage Δ
service/matching/tasklist/task_list_manager.go	63.70% <100.00%> (ø)
service/matching/tasklist/task_reader.go	73.80% <100.00%> (+0.68%)	⬆️
common/cache/lru.go	84.97% <80.00%> (+0.26%)	⬆️

... and 7 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018fd4cd-8372-4140-b2cf-697a6f7bac87

Details

• 30 of 30 (100.0%) changed or added relevant lines in 5 files are covered.
• 59 unchanged lines in 17 files lost coverage.
• Overall coverage decreased (-0.03%) to 69.658%

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Files with Coverage Reduction	New Missed Lines	%
tools/cli/admin_db_decode_thrift.go	1	71.79%
common/task/weighted_round_robin_task_scheduler.go	2	89.05%
common/persistence/execution_manager.go	2	90.46%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
service/history/replication/task_processor.go	2	81.25%
service/history/execution/mutable_state_util.go	2	78.52%
common/membership/hashring.go	2	84.69%
common/persistence/statsComputer.go	2	98.57%
service/matching/tasklist/matcher.go	2	89.35%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%

Totals
Change from base Build 018fd17e-a401-4eba-8372-591d1e581574:	-0.03%
Covered Lines:	103050
Relevant Lines:	147937

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💛 - Coveralls

[3vilhamster]

Good catch