[code-coverage] Add tests for HandleDecisionTaskScheduled API in service/history/decision

[ketsiambaku]

What changed?
Add tests for HandleDecisionTaskScheduled API in service/history/decision

Why?
Code coverage improvements

How did you test it?
unit tests

Potential risks
N/A

Release notes

Documentation Changes

[codecov]

Codecov Report

Merging #5901 (95c28bc) into master (e833741) will increase coverage by 0.05%.
The diff coverage is n/a.

Additional details and impacted files

see 6 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018ec872-14c0-407b-b9b9-95663192c075

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 46 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.02%) to 67.372%

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Files with Coverage Reduction	New Missed Lines	%
service/matching/taskReader.go	2	84.88%
service/matching/matcher.go	2	90.72%
service/history/queue/timer_queue_processor_base.go	3	77.82%
service/history/task/fetcher.go	3	86.6%
common/task/fifo_task_scheduler.go	4	83.51%
service/history/execution/mutable_state_task_refresher.go	32	56.65%

Totals
Change from base Build 018ec712-a05e-4ec1-a66b-6d12d6428fe1:	0.02%
Covered Lines:	98212
Relevant Lines:	145776

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💛 - Coveralls