nextest: mark local tests that last >10s as slow, increase CI SLOW value #6241

Job	Run time
build (no git)	1m 24s
nix flake (ubuntu-24.04)	1m 24s
test (linux-x86_64-gnu)	1m 28s
nix flake (macos-14)	1m 28s
nix flake (ubuntu-24.04-arm)	1m 25s
test (macos-x86_64)	1m 30s
test (linux-aarch64-gnu)	1m 25s
test (macos-aarch64)	1m 29s
test (windows-aarch64)	1m 19s
check (zizmor)	24s
check (latest mkdocs, optional)	16s
check (Cargo.lock dependency count)	3s
check (doctests)	1m 29s
test (windows-x86_64)	1m 16s
check (clippy)	1m 29s
check (protos)	1m 27s
check (codespell)	13s
check (mkdocs)	17s
check (rustfmt)	22s
check (cargo-deny, bans)	23s
check (cargo-deny, licenses)	25s
check (cargo-deny, sources)	29s
check (cargo-deny, advisories)	28s
required checks (merge queue)	1s
	21m 54s

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