`Synthesizer`から`Mutex`を外す #2230

Job	Run time
validate-cargo-lock	36s
actionlint	26s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	6m 50s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	2m 52s
build-windows-cpp-example	6m 59s
c-header	1m 12s
rust-integration-test-strategy-matrix	3s
rust-lint	4m 7s
rust-unit-test	6m 39s
shellcheck	17s
build-and-test-java-api (windows-latest)	10m 32s
build-and-test-java-api (macos-latest)	3m 49s
build-and-test-java-api (ubuntu-latest)	3m 51s
build-and-test-python-api (windows-latest)	11m 2s
build-and-test-python-api (macos-latest)	7m 14s
build-and-test-python-api (ubuntu-latest)	3m 52s
rust-integration-test (windows-2019, directml)	4m 59s
rust-integration-test (macos-11)	3m 8s
rust-integration-test (ubuntu-20.04)	2m 52s
	1h 21m 20s

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