Bump version to `0.18.0+ffmpeg.8.0` #597

Job	Run time
rust_clippy_check_ubuntu	7m 21s
rust_clippy_check_windows	1m 28s
rustfmt_check (windows-latest)	30s
rustfmt_check (macos-latest)	16s
rustfmt_check (ubuntu-latest)	14s
build_dynamic_and_test_windows_pre	8m 11s
build_static_and_test_ubuntu (release/6.0, nightly, no valgrind)	7m 18s
build_static_and_test_ubuntu (release/7.0, nightly, no valgrind)	8m 11s
docs_rs_check	1m 51s
build_static_and_test_ubuntu (release/6.0, 1.81.0, no valgrind)	7m 11s
build_static_and_test_ubuntu (release/7.0, 1.81.0, no valgrind)	7m 26s
build_static_and_test_ubuntu (release/7.1, nightly, no valgrind)	8m 49s
build_static_and_test_ubuntu (release/6.1, 1.81.0, no valgrind)	7m 22s
build_static_and_test_ubuntu (release/6.1, nightly, no valgrind)	7m 21s
build_static_and_test_ubuntu (release/7.1, 1.81.0, valgrind)	7m 11s
build_static_and_test_ubuntu (release/8.0, 1.81.0, valgrind)	7m 44s
build_static_and_test_ubuntu (release/8.0, nightly, no valgrind)	9m 19s
build_static_and_test_ubuntu (release/7.1, 1.81.0, no valgrind)	6m 54s
build_static_and_test_ubuntu (release/8.0, 1.81.0, no valgrind)	9m 19s
build_dynamic_and_test_windows (1.81.0)	1m 28s
build_dynamic_and_test_windows (nightly)	1m 30s
	1h 56m 54s

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