Refactor: extract isSimpleVariableReference() method on IntertwinedVariableByReferenceWithExpr

Move the variable-type checking logic from MutatingScope::invalidateExpression()
into a dedicated method for better readability.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/MutatingScope.php

@@ -2810,10 +2810,7 @@ public function invalidateExpression(Expr $expressionToInvalidate, bool $require
 			$exprExpr = $exprTypeHolder->getExpr();
 			if (
 				$exprExpr instanceof IntertwinedVariableByReferenceWithExpr
-				&& $exprExpr->getExpr() instanceof Variable
-				&& is_string($exprExpr->getExpr()->name)
-				&& $exprExpr->getAssignedExpr() instanceof Variable
-				&& is_string($exprExpr->getAssignedExpr()->name)
+				&& $exprExpr->isSimpleVariableReference()
 			) {
 				continue;
 			}

src/Node/Expr/IntertwinedVariableByReferenceWithExpr.php

@@ -29,6 +29,14 @@ public function getAssignedExpr(): Expr
 		return $this->assignedExpr;
 	}
 
+	public function isSimpleVariableReference(): bool
+	{
+		return $this->expr instanceof \PhpParser\Node\Expr\Variable
+			&& is_string($this->expr->name)
+			&& $this->assignedExpr instanceof \PhpParser\Node\Expr\Variable
+			&& is_string($this->assignedExpr->name);
+	}
+
 	#[Override]
 	public function getType(): string
 	{