[fix] skip all-but standalone assign on SetTypeToCastRector #31602

Job	Run time
Run with Space in Directory	19s
Preload php-parser Order	22s
Check fixture classes are different to nodes	20s
PHPStan	1m 24s
Active Classes	22s
Check before/after test fixture on no-changes	23s
Compatible PHPStan versions	24s
Commented Code	22s
Detect composer dependency issues	27s
Check no "*.php" files in rules Fixture directory	18s
Help and Version	16s
Composer Validate	22s
PHP Linter	28s
Finalize classes	23s
	6m 10s

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