Bump google.golang.org/grpc in /grpc/examples/go/greeter/server (#8132)

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.53.0 to 1.56.3.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.53.0...v1.56.3)

---
updated-dependencies:
- dependency-name: google.golang.org/grpc
  dependency-type: direct:production
...

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grpc/examples/go/greeter/server/go.mod

@@ -5,7 +5,7 @@ go 1.15
 replace github.com/google/flatbuffers/grpc/examples/go/greeter/models v0.0.0 => ../models
 
 require (
-	github.com/google/flatbuffers v1.12.0
+	github.com/google/flatbuffers v2.0.8+incompatible
 	github.com/google/flatbuffers/grpc/examples/go/greeter/models v0.0.0
-	google.golang.org/grpc v1.53.0
+	google.golang.org/grpc v1.56.3
 )