[Vendor] upgrade google/go-github to v32.1.0 (#12361)

* upgrate go-github client to v32.1.0

* migrate

vendor/github.com/google/go-github/v32/github/git.go

@@ -0,0 +1,12 @@
+// Copyright 2013 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package github
+
+// GitService handles communication with the git data related
+// methods of the GitHub API.
+//
+// GitHub API docs: https://developer.github.com/v3/git/
+type GitService service