Fix a race condition in VAAPI CSC to YUV420P #1136

Job	Run time
build_portable_mac / Build Portable FFmpeg (macos-13, x86_64)	40m 57s
build_portable_mac / Build Portable FFmpeg (macos-14, arm64)	22m 44s
build_portable_windows / Build Portable FFmpeg (win64)	37m 16s
build_debian / Build FFmpeg (bullseye, amd64)	55m 34s
build_portable_linux / Build Portable FFmpeg (amd64)	1h 46m 20s
build_debian / Build FFmpeg (bullseye, arm64)	14m 49s
build_portable_linux / Build Portable FFmpeg (arm64)	1h 39m 40s
build_portable_windows_clang / Build Portable FFmpeg (CLANG64, win64)	1h 7m 34s
build_ubuntu / Build FFmpeg (focal, amd64)	1h 4m 41s
build_debian / Build FFmpeg (bullseye, armhf)	13m 40s
build_ubuntu / Build FFmpeg (focal, arm64)	15m 36s
build_debian / Build FFmpeg (bookworm, amd64)	1h 5m 58s
build_ubuntu / Build FFmpeg (focal, armhf)	13m 56s
build_debian / Build FFmpeg (bookworm, arm64)	14m 30s
build_debian / Build FFmpeg (bookworm, armhf)	13m 20s
build_ubuntu / Build FFmpeg (jammy, amd64)	58m 12s
build_ubuntu / Build FFmpeg (jammy, arm64)	17m 44s
build_ubuntu / Build FFmpeg (jammy, armhf)	13m 29s
build_ubuntu / Build FFmpeg (noble, amd64)	58m 19s
build_ubuntu / Build FFmpeg (noble, arm64)	16m 30s
build_ubuntu / Build FFmpeg (noble, armhf)	15m 22s
build_portable_windows / Publish Portable Release	0s
build_portable_mac / Publish Portable Release	0s
build_ubuntu / Publish Release	0s
build_debian / Publish Release	0s
build_portable_windows_clang / Publish Portable Release	0s
build_portable_linux / Publish Portable Release	0s
	13h 46m 11s

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