Tests: Various harness improvements, especially on Windows #732

Job	Run time
code-quality / PHPCS	21s
code-quality / Lint GitHub Actions workflows	4s
code-quality / PHPStan	22s
code-quality / Lint PHP files	22s
code-quality / Spell check	7s
code-quality / Lint Gherkin Feature files	16s
	1m 32s

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