[dx] warn about deprecated beforeTraverse() method once FileNode is ready #31826

Job	Run time
Compatible PHPStan versions	16s
Preload php-parser Order	19s
Check before/after test fixture on no-changes	21s
Active Classes	30s
Run with Space in Directory	28s
Composer Validate	21s
Commented Code	23s
Check no "*.php" files in rules Fixture directory	20s
PHP Linter	24s
Help and Version	18s
PHPStan	1m 21s
Check fixture classes are different to nodes	19s
Detect composer dependency issues	19s
Finalize classes	21s
	6m 0s

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