Bump Google.Protobuf from 3.11.4 to 3.15.0 in /tests/Envoy.Control.Runner#2

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dependabot/nuget/tests/Envoy.Control.Runner/Google.Protobuf-3.15.0ahmelsayed/envoy-csharp-control-plane:dependabot/nuget/tests/Envoy.Control.Runner/Google.Protobuf-3.15.0Copy head branch name to clipboard