Fix and rename sig_scheme_to_nid #293

Job	Run time
Clang Tidy	6s
Clippy	31s
Clippy nightly (optional)	33s
Build+test (stable, ubuntu-latest)	1m 47s
Build+test (stable, ubuntu-22.04)	1m 47s
Check for documentation errors	43s
Format	13s
Build+test (beta, ubuntu-latest)	1m 46s
Miri	1m 2s
Build+test (beta, ubuntu-22.04)	1m 41s
Packaging	3m 3s
Build+test (nightly, ubuntu-latest)	1m 48s
Produce release packages (fedora, 40, rpm)	3m 10s
Valgrind	2m 20s
Build+test (nightly, ubuntu-22.04)	1m 40s
Produce release packages (ubuntu, 24.04, deb)	2m 5s
	24m 15s

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