Update protobuf library to v.3.6.1.2.
Update protobuf library to v.3.6.1.2.

This is required to make the build work with the newest bazel binary. See https://github.com/protocolbuffers/protobuf/issues/5418

PiperOrigin-RevId: 227681358
GitOrigin-RevId: 1df09b7dbe849a527f2da882e96483f3e967a26b

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