tools: build with -mod=readonly

tools/build.sh

@@ -1,8 +1,8 @@
 #!/bin/bash
 set -e
 
-go build -o bin/protoc-gen-go google.golang.org/protobuf/cmd/protoc-gen-go
-go build -o bin/protoc-gen-go-grpc google.golang.org/grpc/cmd/protoc-gen-go-grpc
-go build -o bin/buf github.com/bufbuild/buf/cmd/buf
-go build -o bin/cobra github.com/spf13/cobra/cobra
+go build -mod=readonly -o bin/protoc-gen-go google.golang.org/protobuf/cmd/protoc-gen-go
+go build -mod=readonly -o bin/protoc-gen-go-grpc google.golang.org/grpc/cmd/protoc-gen-go-grpc
+go build -mod=readonly -o bin/buf github.com/bufbuild/buf/cmd/buf
+go build -mod=readonly -o bin/cobra github.com/spf13/cobra/cobra