[fix] skip all-but standalone assign on SetTypeToCastRector #31604

Job	Run time
Composer Validate	22s
Preload php-parser Order	20s
PHPStan	1m 30s
Help and Version	22s
Run with Space in Directory	24s
Commented Code	30s
Active Classes	21s
Check before/after test fixture on no-changes	22s
Finalize classes	25s
Check no "*.php" files in rules Fixture directory	25s
PHP Linter	35s
Compatible PHPStan versions	20s
Detect composer dependency issues	24s
Check fixture classes are different to nodes	23s
	6m 43s

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