Fix and rename sig_scheme_to_nid #295

Job	Run time
Clang Tidy	7s
Clippy	36s
Clippy nightly (optional)	31s
Build+test (stable, ubuntu-latest)	1m 2s
Check for documentation errors	40s
Build+test (stable, ubuntu-22.04)	1m 1s
Format	16s
Miri	1m 3s
Build+test (beta, ubuntu-latest)	1m 9s
Build+test (beta, ubuntu-22.04)	59s
Packaging	3m 13s
Build+test (nightly, ubuntu-latest)	1m 9s
Produce release packages (fedora, 40, rpm)	2m 47s
Valgrind	2m 16s
Build+test (nightly, ubuntu-22.04)	55s
Produce release packages (ubuntu, 24.04, deb)	2m 8s
	19m 52s

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