fix: add InsecureCredentials to address issue in Cloud Spanner emulat…

…or (#5224)

src/EmulatorTrait.php

@@ -44,7 +44,8 @@ private function emulatorGapicConfig($emulatorHost)
                         'credentials' => \Grpc\ChannelCredentials::createInsecure()
                     ]
                 ]
-            ]
+            ],
+            'credentials' => new InsecureCredentialsWrapper(),
         ];
     }
     /**

src/InsecureCredentialsWrapper.php

@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * Copyright 2022 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Google\Cloud\Core;
+
+use Google\ApiCore\CredentialsWrapper;
+
+/**
+ * For connect to emulator.
+ */
+class InsecureCredentialsWrapper extends CredentialsWrapper
+{
+    public function __construct()
+    {
+    }
+
+    public function getAuthorizationHeaderCallback($audience = null)
+    {
+        return null;
+    }
+}