Add unit tests for mutable state task refresher

[Shaddoll]

What changed?
Add unit tests for mutable state task refresher

Why?
improve coverage

How did you test it?
unit tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.20%. Comparing base (2ac145f) to head (5f7f6c0).
Report is 1 commits behind head on master.

❗ Current head 5f7f6c0 differs from pull request most recent head 0fbc282. Consider uploading reports for the commit 0fbc282 to get more accurate results

Additional details and impacted files

Files	Coverage Δ
.../history/execution/mutable_state_task_refresher.go	92.59% <100.00%> (+89.81%)	⬆️

... and 4 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018f54b1-eea9-4732-b8ae-65a3e24128be

Details

• 59 of 59 (100.0%) changed or added relevant lines in 1 file are covered.
• 52 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.08%) to 68.269%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	2	88.06%
service/history/handler/handler.go	2	60.71%
service/matching/taskListManager.go	2	81.16%
common/asyncworkflow/queue/consumer/default_consumer.go	3	92.13%
common/persistence/statsComputer.go	3	96.79%
common/archiver/filestore/historyArchiver.go	4	80.95%
service/frontend/api/handler.go	6	62.14%
service/history/engine/engineimpl/poll_mutable_state.go	9	74.16%
service/frontend/wrappers/metered/metered.go	9	63.18%
service/history/task/transfer_standby_task_executor.go	12	85.8%

Totals
Change from base Build 018f54af-1427-4fbc-bc5d-7b9472685578:	0.08%
Covered Lines:	100281
Relevant Lines:	146892

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💛 - Coveralls