Add PHP 8.3 support (#20) (#21) #43

Job	Run time
PHPSpec tests (lowest, 8.0, ubuntu-latest)	13s
PHPSpec tests (lowest, 8.0, windows-latest)	38s
PHPSpec tests (lowest, 8.1, ubuntu-latest)	13s
PHPSpec tests (lowest, 8.1, windows-latest)	44s
PHPSpec tests (lowest, 8.2, ubuntu-latest)	15s
PHPSpec tests (lowest, 8.2, windows-latest)	45s
PHPSpec tests (lowest, 8.3, ubuntu-latest)	11s
PHPSpec tests (lowest, 8.3, windows-latest)	35s
PHPSpec tests (highest, 8.0, ubuntu-latest)	10s
PHPSpec tests (highest, 8.0, windows-latest)	36s
PHPSpec tests (highest, 8.1, ubuntu-latest)	9s
PHPSpec tests (highest, 8.1, windows-latest)	46s
PHPSpec tests (highest, 8.2, ubuntu-latest)	16s
PHPSpec tests (highest, 8.2, windows-latest)	44s
PHPSpec tests (highest, 8.3, ubuntu-latest)	18s
PHPSpec tests (highest, 8.3, windows-latest)	32s
PHPSpec tests (locked, 8.0, ubuntu-latest)	16s
PHPSpec tests (locked, 8.0, windows-latest)	41s
PHPSpec tests (locked, 8.1, ubuntu-latest)	11s
PHPSpec tests (locked, 8.1, windows-latest)	41s
PHPSpec tests (locked, 8.2, ubuntu-latest)	13s
PHPSpec tests (locked, 8.2, windows-latest)	45s
PHPSpec tests (locked, 8.3, ubuntu-latest)	16s
PHPSpec tests (locked, 8.3, windows-latest)	34s
	10m 42s

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