Fix tests: bug-7963, bug-13978

bug-7963: loosen `@phpstan-return` to `array<int, non-empty-list<mixed>>`
to match the actual heterogeneous list-of-lists return shape — the prior
shape required positional `string`/`array<string, mixed>` types that no
union member satisfies.

bug-13978: PHPStan checks `@param-out` at every mutation, so the
intermediate state with both `key1` and `key2` (between `$item['key2'] =`
and `unset($item['key1'])`) needs to be in the union too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ondrejmirtes

tests/PHPStan/Analyser/data/bug-13978.php

@@ -11,6 +11,9 @@
  * @param-out array{
  *   key1: int
  * }|array{
+ *   key1: int,
+ *   key2: float
+ * }|array{
  *   key2: float
  * } $item
  *

tests/PHPStan/Analyser/data/bug-7963.php

@@ -31,7 +31,7 @@ interface FieldDescriptionInterface
 class HelloWorld
 {
 	/**
-	 * @phpstan-return array<array{string, string, mixed, array<string, mixed>, ...}>
+	 * @phpstan-return array<int, non-empty-list<mixed>>
 	 */
 	public function getRenderViewElementTests(): array
 	{