Add note comment about unescaped \ on SimplifyRegexPatternRector #30719

Job	Run time
Run with Space in Directory	22s
Help and Version	24s
Preload php-parser Order	26s
Commented Code	28s
PHPStan	1m 24s
Active Classes	18s
Finalize classes	24s
Compatible PHPStan versions	21s
Check no "*.php" files in rules Fixture directory	27s
Check before/after test fixture on no-changes	16s
Detect composer dependency issues	25s
Composer Validate	18s
	5m 33s

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