Add a QUIC test for back pressure #813

Job	Run time
basic_clang	7m 11s
basic_gcc	8m 46s
check_docs	1m 19s
check_update	2m 16s
check-ansi	4m 10s
minimal	4m 16s
no-deprecated	8m 17s
no-shared (ubuntu-latest)	5m 25s
no-shared (macos-latest)	8m 39s
address_ub_sanitizer	14m 43s
buildtest	11m 30s
enable_brotli_and_asan_ubsan	12m 54s
enable_brotli_and_zstd_dynamic	7m 4s
enable_brotli_dynamic	7m 24s
enable_non-default_options	7m 47s
enable_zstd_and_asan_ubsan	16m 45s
enable_zstd_dynamic	7m 34s
enable-tfo (ubuntu-latest)	6m 59s
enable-tfo (macos-latest)	11m 6s
external-test-cf-quiche	5m 50s
external-test-pyca (1.51.0, 3.9)	10m 46s
external-tests	4m 29s
fips_and_ktls	10m 30s
legacy	5m 52s
memory_sanitizer	22m 23s
no-legacy	7m 40s
non-caching	22m 2s
out-of-source-and-install (ubuntu-latest)	11m 52s
out-of-source-and-install (macos-latest)	16m 51s
threads_sanitizer	5m 45s
	4h 38m 5s

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