Bump version to `0.15.0+ffmpeg.7.0` #348

Job	Run time
build_dynamic_and_test_ubuntu	1m 43s
build_dynamic_and_test_windows_pre	2m 40s
build_static_and_test_ubuntu	5m 50s
build_dynamic_and_test_macos	1m 52s
build_static_and_test_ubuntu_with_system_ffmpeg	1m 46s
build_with_vcpkg_ffmpeg_windows (x86_64-pc-windows-msvc, x64-windows-static, -Ctarget-feature=+cr...	21m 59s
docs_rs_check	1m 7s
build_with_vcpkg_ffmpeg_windows (x86_64-pc-windows-msvc, x64-windows-static-md)	20m 46s
rust_clippy_check_ubuntu	5m 45s
build_with_vcpkg_ffmpeg_windows (x86_64-pc-windows-msvc, x64-windows, true)	22m 15s
rust_clippy_check_windows	19m 10s
build_with_vcpkg_ffmpeg_windows (i686-pc-windows-msvc, x86-windows-static, -Ctarget-feature=+crt-...	20m 47s
rustfmt_check (macos-latest)	8s
build_with_vcpkg_ffmpeg_windows (i686-pc-windows-msvc, x86-windows-static-md)	20m 48s
rustfmt_check (windows-latest)	15s
build_with_vcpkg_ffmpeg_windows (i686-pc-windows-msvc, x86-windows, true)	20m 57s
rustfmt_check (ubuntu-latest)	5s
build_dynamic_and_test_windows	1m 35s
	2h 49m 28s

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