chore: bump version to 2.8.1 #2559

Job	Run time
builds / create-api-matrix	12s
builds / create-phpunit-matrix	7s
builds / unit tests and linting (stable27, 8.0, 8, 0, mysql)	1m 10s
builds / unit tests and linting (stable28, 8.1, 8, 1, mysql)	1m 16s
builds / unit tests and linting (stable29, 8.1, 8, 1, mysql)	1m 13s
builds / unit tests and linting (stable30, 8.2, 8, 2, mysql)	1m 16s
builds / unit tests and linting (stable31, 8.1, 8, 1, mysql)	1m 5s
builds / unit tests and linting (stable31, 8.2, 8, 2, mysql)	1m 8s
builds / unit tests and linting (stable31, 8.3, 8, 3, mysql)	1m 6s
builds / API tests (stable27, 8.0, 8, 0, mysql)	58s
builds / API tests (stable28, 8.1, 8, 1, mysql)	1m 1s
builds / API tests (stable29, 8.1, 8, 1, mysql)	1m 3s
builds / API tests (stable30, 8.2, 8, 2, mysql)	1m 0s
builds / API tests (stable31, 8.1, 8, 1, mysql)	1m 1s
builds / API tests (stable31, 8.2, 8, 2, mysql)	59s
builds / API tests (stable31, 8.3, 8, 3, mysql)	58s
builds / API tests (stable31, 8.2, 8, 2, pgsql)	1m 0s
builds / notify-nightly-report	1s
	16m 34s

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