Migrate coverage reporting from Coveralls to Codecov #93

Job	Run time
Coding Standard / Coding Standard (PHP 8.2)	14s
PHPUnit (8.5, highest)	19s
PHPUnit (8.3, highest)	20s
PHPUnit (8.2, highest)	19s
PHPUnit (8.2, lowest)	15s
PHPUnit (8.4, highest)	18s
Psalm	24s
	2m 9s

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