Bump actions/download-artifact from 4.1.9 to 4.2.1 #2511

Job	Run time
env-protect-setup	4s
authorize	1s
get-dev-image / get-image	5s
clang-tidy	1m 2s
generate-matrix	3m 23s
code-coverage	0s
build-and-test (Clang opt + UI, nokvm, --config=clang --compilation_mode=opt, bazel_buildables_cl...	6m 31s
build-and-test (Clang debug, nokvm, --config=clang --compilation_mode=dbg, bazel_buildables_clang...	4m 25s
build-and-test (ASAN, nokvm, --config=asan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	4m 34s
build-and-test (TSAN, nokvm, --config=tsan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	4m 21s
build-and-test (GCC opt, nokvm, --config=gcc --compilation_mode=opt, bazel_buildables_gcc_opt, ba...	5m 15s
build-and-test (Go race detector, nokvm, --config=go_race --compilation_mode=opt, bazel_buildable...	3m 10s
build-and-test-status	1s
	32m 52s

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