fix AssertIsTypeMethodCallRector crash on enum case argument

[TomasVotruba]

Summary

• Fixes a fatal crash in AssertIsTypeMethodCallRector when isType() is called with an enum case argument inside a TestCase subclass
• Adds a is_string() guard before using the resolved arg value as an array key in isset()
• Adds a skip fixture to cover the non-string arg scenario

Root cause

ValueResolver::getValue() returns the enum case object itself for enum arguments. Using it as an array key in isset(self::IS_TYPE_VALUE_TO_METHOD[$argValue]) caused:

System error: "Cannot access offset of type App\Enums\SomeEnum in isset or empty"

Fix

Added an is_string($argValue) guard immediately after resolving the argument value. Non-string values can never match any key in IS_TYPE_VALUE_TO_METHOD, so returning null early is both correct and safe.

Fixes rectorphp/rector#9765

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Generated by Claude Code

[TomasVotruba]

Looks good 👌

[Levivb]

not really though ;)

although the actual crash is fixed, the underlying issue is that isType is processed regardless of the classtype the method is called on.

- (new stdClass)->isType('array');
+ (new stdClass)->isArray();

[TomasVotruba]

2 bugs in one :)