Fix InspectorTypeExtension compatibility with PHPStan 2.1.47 mixed~null type (#976)

PHPStan 2.1.47 now infers mixed~null instead of mixed in certain scopes.
Update the assertAll check to use instanceof MixedType rather than equals()
so mixed~null inputs are also narrowed to iterable.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mglaman

src/Type/InspectorTypeExtension.php

@@ -111,7 +111,7 @@ private function specifyAssertAll(MethodReflection $staticMethodReflection, Stat
         // If it is already not mixed (narrowed by other code, like
         // '::assertAllArray()'), we could not provide any additional
         // information. We can only narrow this method to 'array<mixed, mixed>'.
-        if (!$traversableType->equals(new MixedType())) {
+        if (!$traversableType instanceof MixedType) {
             return new SpecifiedTypes();
         }
 

tests/src/Type/data/bug-857.php

@@ -14,7 +14,7 @@ function mixed_function(): mixed {}
 
 // If the type is narrowed before '::assertAll()', it shouldn't change it.
 $array = mixed_function();
-assertType('mixed', $array);
+assertType('mixed~null', $array);
 \assert(Inspector::assertAllArrays($array));
 assertType('iterable<array>', $array);
 \assert(Inspector::assertAll(fn (array $i): bool => TRUE, $array));