Add tests for ForkHistoryBranch

[jakobht]

What changed?
Tests for fork history branch

Why?

How did you test it?

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018f1618-17b6-4049-abd3-e4a402a18dc8

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 24 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.02%) to 67.746%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weighted_round_robin_task_scheduler.go	1	89.05%
common/persistence/sql/sqlplugin/postgres/task.go	2	73.4%
common/persistence/sql/sqlplugin/postgres/db.go	2	80.0%
common/task/fifo_task_scheduler.go	2	87.63%
service/history/queue/timer_queue_processor_base.go	3	77.82%
service/history/execution/mutable_state_task_refresher.go	14	64.56%

Totals
Change from base Build 018f127b-cd0f-43c3-b47a-35b58b7623db:	0.02%
Covered Lines:	99370
Relevant Lines:	146680

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💛 - Coveralls

[davidporter-id-au]

Looks good to me, though I'm not quite confident enough with history to feel super firm being the only stamp. @Shaddoll any thoughts?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.59%. Comparing base (0b41007) to head (e84579f).
Report is 1 commits behind head on master.

❗ Current head e84579f differs from pull request most recent head 84da703. Consider uploading reports for the commit 84da703 to get more accurate results

Additional details and impacted files

see 7 files with indirect coverage changes

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