Fix oneof message in array constructor (#5727)

diff --git a/php/tests/generated_class_test.php b/php/tests/generated_class_test.php
index 93b7b29..a9ad793 100644
--- a/php/tests/generated_class_test.php
+++ b/php/tests/generated_class_test.php
@@ -1447,6 +1447,20 @@
         }
     }
 
+    public function testOneofMessageInArrayConstructor()
+    {
+        $m = new TestMessage([
+            'oneof_message' => new Sub(),
+        ]);
+    }
+
+    public function testOneofStringInArrayConstructor()
+    {
+        $m = new TestMessage([
+            'oneof_string' => 'abc',
+        ]);
+    }
+
     #########################################################
     # Test message equals.
     #########################################################