test: refactor OpenProjectAPIService class unit tests #2356

Job	Run time
builds / unit tests and linting (stable31, 8.1, false)	2m 37s
builds / API tests (stable31, 8, 1, mysql, false)	14m 16s
builds / unit tests and linting (stable31, 8.2, false)	2m 14s
builds / API tests (stable31, 8, 2, mysql, false)	14m 10s
builds / unit tests and linting (stable31, 8.3, false)	2m 26s
builds / API tests (stable31, 8, 3, mysql, false)	13m 30s
builds / unit tests and linting (master, 8.3, false)	2m 20s
builds / API tests (master, 8, 3, mysql, false)	13m 47s
builds / unit tests and linting (stable27, 8)	2m 9s
builds / API tests (stable31, 8, 1, pgsql)	14m 46s
builds / unit tests and linting (stable28, 8.1)	2m 40s
builds / API tests (stable27, 8, 0, mysql)	14m 3s
builds / unit tests and linting (stable29, 8.1)	3m 6s
builds / API tests (stable28, 8, 1, mysql)	13m 52s
builds / unit tests and linting (stable30, 8.2)	2m 20s
builds / API tests (stable29, 8, 1, mysql)	14m 16s
builds / API tests (stable30, 8, 2, mysql)	14m 14s
builds / notify-nightly-report	0s
	2h 26m 46s

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