h3: set stream priority after headers buffered #5141

Job	Run time
http3_test	46s
quiche	3m 44s
quiche_ios (x86_64-apple-ios)	1m 9s
quiche (boringssl-boring-crate)	3m 42s
quiche_ios (aarch64-apple-ios)	1m 6s
quiche_macos (macos-13)	3m 35s
quiche (openssl)	5m 55s
quiche_macos (macos-latest)	2m 18s
quiche_multiarch (aarch64-unknown-linux-gnu)	2m 56s
quiche_windows (x86_64-pc-windows-msvc)	3m 43s
quiche_multiarch (armv7-unknown-linux-gnueabihf)	3m 14s
quiche_windows (i686-pc-windows-msvc)	2m 54s
quiche_multiarch (i686-unknown-linux-gnu)	1m 53s
quiche_windows (x86_64-pc-windows-gnu)	4m 47s
quiche_windows (i686-pc-windows-gnu)	5m 15s
android_ndk_lts (aarch64-linux-android)	58s
android_ndk_lts (armv7-linux-androideabi)	56s
docker	2m 37s
android_ndk_lts (x86_64-linux-android)	1m 4s
nginx (1.16.1)	58s
android_ndk_lts (i686-linux-android)	55s
	54m 25s

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