build: update secrets configuration (#395)

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packages/google-cloud-dns/synth.metadata

@@ -3,8 +3,15 @@
     {
       "git": {
         "name": ".",
-        "remote": "git@github.com:googleapis/nodejs-dns.git",
-        "sha": "68fbc61d8812221c6d25536a6a5e6563128b6ebb"
+        "remote": "https://github.com/googleapis/nodejs-dns.git",
+        "sha": "4d3051f0bb9561965d5836e472a6f93c46b49385"
+      }
+    },
+    {
+      "git": {
+        "name": "synthtool",
+        "remote": "https://github.com/googleapis/synthtool.git",
+        "sha": "f13864cd532f98a4682cec48105580fa9a5c9978"
       }
     }
   ]