clean: silence CMake warning from Abseil configs (#4725)
clean: silence CMake warning from Abseil configs (#4725)

This problem is explained in #4146, this PR silences the warning
generated by an indirect find_package(absl) through find_package(gRPC)

googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp