test: refactor OpenProjectAPIService class unit tests #2359

Job	Run time
builds / API tests (stable31, 8, 1, mysql, false)	14m 23s
builds / API tests (stable31, 8, 2, mysql, false)	14m 42s
builds / API tests (stable31, 8, 3, mysql, false)	13m 35s
builds / unit tests and linting (stable31, 8.1, false)	2m 20s
builds / API tests (master, 8, 3, mysql, false)	13m 13s
builds / unit tests and linting (stable31, 8.2, false)	2m 37s
builds / API tests (stable31, 8, 1, pgsql)	14m 49s
builds / unit tests and linting (stable31, 8.3, false)	2m 28s
builds / API tests (stable27, 8, 0, mysql)	14m 13s
builds / unit tests and linting (master, 8.3, false)	2m 31s
builds / API tests (stable28, 8, 1, mysql)	14m 6s
builds / unit tests and linting (stable27, 8)	2m 8s
builds / API tests (stable29, 8, 1, mysql)	14m 30s
builds / unit tests and linting (stable28, 8.1)	2m 27s
builds / API tests (stable30, 8, 2, mysql)	14m 13s
builds / unit tests and linting (stable29, 8.1)	3m 1s
builds / unit tests and linting (stable30, 8.2)	2m 19s
builds / notify-nightly-report	0s
	2h 27m 35s

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