Allow magic methods named "as"

Fixes #2881

src/Psalm/Internal/Type/ParseTree.php

@@ -473,6 +473,7 @@ class ParseTree
                     break;
 
                 case 'as':
+                    if ($i > 0) {
                         $current_parent = $current_leaf->parent;
 
                         if (!$current_leaf instanceof ParseTree\Value
@@ -494,6 +495,7 @@ class ParseTree
                         ++$i;
 
                         break;
+                    }
 
                 default:
                     $new_parent = !$current_leaf instanceof ParseTree\Root ? $current_leaf : null;

tests/MagicMethodAnnotationTest.php

@@ -576,6 +576,13 @@ class MagicMethodAnnotationTest extends TestCase
                         return B::make();
                     }'
             ],
+            'validMethodAsAnnotation' => [
+                '<?php
+                    /**
+                     * @method string as(string $value)
+                     */
+                    class Foo {}'
+            ],
         ];
     }