bug symfony#61580 [JsonStreamer] Fix encoding iterable lists (mtarld)

This PR was merged into the 7.3 branch.

Discussion
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[JsonStreamer] Fix encoding iterable lists

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

Sibling of symfony#61561.

Handle any iterable with `int` as key as a list during encoding (which mean being encoded with brackets).

Commits
-------

2057bc8 [JsonStreamer] Fix encoding iterable lists

Author: fabpot

src/Symfony/Component/JsonStreamer/Tests/JsonStreamWriterTest.php

@@ -105,7 +105,7 @@ public function testWriteCollection()
         );
 
         $this->assertWritten(
-            '{"0":{"id":1,"name":"dummy"},"1":{"id":1,"name":"dummy"}}',
+            '[{"id":1,"name":"dummy"},{"id":1,"name":"dummy"}]',
             new \ArrayObject([new ClassicDummy(), new ClassicDummy()]),
             Type::iterable(Type::object(ClassicDummy::class), Type::int()),
         );

src/Symfony/Component/JsonStreamer/Write/PhpAstBuilder.php

@@ -294,7 +294,9 @@ private function buildYieldStatements(DataModelNodeInterface $dataModelNode, arr
         if ($dataModelNode instanceof CollectionNode) {
             ++$context['depth'];
 
-            if ($dataModelNode->getType()->isList()) {
+            $collectionKeyType = $dataModelNode->getType()->getCollectionKeyType();
+
+            if ($collectionKeyType instanceof BuiltinType && TypeIdentifier::INT === $collectionKeyType->getTypeIdentifier()) {
                 return [
                     new Expression(new Yield_($this->builder->val('['))),
                     new Expression(new Assign($this->builder->var('prefix'), $this->builder->val(''))),