Tests

Fix linter issues and bump symfony dev-dependencies #28

Job	Run time
Tests (8.4, windows-latest, prefer-stable)	44s
Tests (8.4, macos-latest, prefer-stable)	52s
Tests (8.5, windows-latest, prefer-stable)	52s
Tests (8.4, windows-latest, prefer-lowest)	46s
Tests (8.5, ubuntu-latest, prefer-stable)	31s
Tests (8.4, macos-latest, prefer-lowest)	1m 15s
Tests (8.4, ubuntu-latest, prefer-lowest)	20s
Tests (8.5, ubuntu-latest, prefer-lowest)	19s
Tests (8.4, ubuntu-latest, prefer-stable)	21s
Tests (8.5, macos-latest, prefer-lowest)	1m 5s
Tests (8.5, macos-latest, prefer-stable)	55s
Tests (8.5, windows-latest, prefer-lowest)	53s
	8m 53s

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