Replace old Codex link in documentation #167

Job	Run time
code-quality / PHPStan	23s
code-quality / PHPCS	21s
code-quality / Spell check	5s
code-quality / Lint GitHub Actions workflows	8s
code-quality / Lint Gherkin Feature files	16s
code-quality / Lint PHP files	20s
	1m 33s

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