feat: drop support for PHP < 8.1 #246

Job	Run time
Coding Standards (8.1, highest)	13s
Code Coverage (8.2, highest)	38s
Dependency Analysis (8.1, highest, ^5.4)	23s
Unit tests (8.1, lowest, ^5.4)	16s
Dependency Analysis (8.1, highest, ^6.0)	23s
Static Code Analysis (8.1, highest, ^5.4)	21s
Unit tests (8.1, lowest, ^6.0)	18s
Dependency Analysis (8.2, highest, ^5.4)	21s
Static Code Analysis (8.1, highest, ^6.0)	24s
Dependency Analysis (8.2, highest, ^6.0)	22s
Unit tests (8.1, highest, ^5.4)	15s
Static Code Analysis (8.2, highest, ^5.4)	22s
Dependency Analysis (8.3, highest, ^5.4)	35s
Unit tests (8.1, highest, ^6.0)	21s
Dependency Analysis (8.3, highest, ^6.0)	29s
Static Code Analysis (8.2, highest, ^6.0)	25s
Unit tests (8.2, lowest, ^5.4)	2m 29s
Static Code Analysis (8.3, highest, ^5.4)	18s
Unit tests (8.2, lowest, ^6.0)	25s
Static Code Analysis (8.3, highest, ^6.0)	22s
Unit tests (8.2, highest, ^5.4)	25s
Unit tests (8.2, highest, ^6.0)	24s
Unit tests (8.3, lowest, ^5.4)	16s
Unit tests (8.3, lowest, ^6.0)	27s
Unit tests (8.3, highest, ^5.4)	28s
Unit tests (8.3, highest, ^6.0)	2m 35s
	14m 15s

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