fixed errant itemgroup element in C# test project (#6854)
fixed errant itemgroup element in C# test project (#6854)

errant save
alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,google/flatbuffers,google/flatbuffers,google/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,google/flatbuffers,alexames/flatbuffers,google/flatbuffers,google/flatbuffers,google/flatbuffers,google/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,google/flatbuffers