Fix a race condition in VAAPI CSC to YUV420P #1131

Job	Run time
build_portable_windows / Build Portable FFmpeg (win64)	35m 22s
build_debian / Build FFmpeg (bullseye, amd64)	35m 23s
build_portable_mac / Build Portable FFmpeg (macos-13, x86_64)	35m 31s
build_debian / Build FFmpeg (bullseye, arm64)	14m 37s
build_portable_linux / Build Portable FFmpeg (amd64)	35m 22s
build_debian / Build FFmpeg (bullseye, armhf)	13m 32s
build_portable_windows_clang / Build Portable FFmpeg (CLANG64, win64)	30m 28s
build_portable_mac / Build Portable FFmpeg (macos-14, arm64)	20m 20s
build_portable_linux / Build Portable FFmpeg (arm64)	35m 21s
build_debian / Build FFmpeg (bookworm, amd64)	40m 6s
build_debian / Build FFmpeg (bookworm, arm64)	14m 46s
build_ubuntu / Build FFmpeg (focal, amd64)	35m 21s
build_debian / Build FFmpeg (bookworm, armhf)	13m 32s
build_ubuntu / Build FFmpeg (focal, arm64)	16m 20s
build_ubuntu / Build FFmpeg (focal, armhf)	15m 10s
build_ubuntu / Build FFmpeg (jammy, amd64)	35m 21s
build_ubuntu / Build FFmpeg (jammy, arm64)	15m 27s
build_ubuntu / Build FFmpeg (jammy, armhf)	13m 28s
build_ubuntu / Build FFmpeg (noble, amd64)	35m 22s
build_ubuntu / Build FFmpeg (noble, arm64)	16m 23s
build_ubuntu / Build FFmpeg (noble, armhf)	14m 51s
build_portable_windows_clang / Publish Portable Release	0s
build_portable_windows / Publish Portable Release	1s
build_portable_linux / Publish Portable Release	1s
build_ubuntu / Publish Release	1s
build_portable_mac / Publish Portable Release	1s
build_debian / Publish Release	1s
	8h 42m 8s

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