Add decoder fuzzer #21

Job	Run time
address_ub_sanitizer	1s
basic_clang	1s
basic_gcc	1s
buildtest	1s
check_docs	1s
check_update	1s
check-ansi	1s
enable_brotli_and_asan_ubsan	1s
enable_brotli_and_zstd_dynamic	1s
enable_brotli_dynamic	1s
enable_non-default_options	1s
enable_zstd_and_asan_ubsan	1s
enable_zstd_dynamic	1s
enable-tfo (ubuntu-latest)	1s
enable-tfo (macos-latest)	1s
external-test-cf-quiche	1s
external-test-pyca (1.51.0, 3.9)	1s
external-tests	1s
fips_and_ktls	1s
legacy	1s
memory_sanitizer	1s
minimal	1s
no-deprecated	1s
no-legacy	1s
non-caching	1s
no-shared (ubuntu-latest)	1s
no-shared (macos-latest)	1s
out-of-source-and-install (ubuntu-latest)	1s
out-of-source-and-install (macos-latest)	1s
threads_sanitizer	1s
	30s

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