Fix namespaces to comply with PSR-4 #1496

Job	Run time
PHP-Linter (8.6) / linter	18s
PHP-Linter (8.5) / linter	8s
Linter / json-linter	24s
Linter / yaml-linter	8s
Linter / ecmascript-linter	-1s
Linter / style-linter	-1s
Unit tests, PHP ${{ matrix.php-versions }}, ${{ matrix.operating-system }}	-1s
Security checks	0s
Unit tests, PHP ${{ matrix.php-versions }}, ${{ matrix.operating-system }}	-1s
Quality control	0s
Code coverage	0s
Cleanup artifacts	0s
	54s

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