Tests

Make Scalar::from_bytes work for Scalar<_, NonZero> #741

Job	Run time
Rustfmt	13s
doc-build	15s
build	19s
clippy_check	21s
test (x86_64-unknown-linux-gnu)	45s
test-alloc (secp256kfun)	49s
test (armv7-unknown-linux-gnueabihf)	5m 43s
test-minimal (secp256kfun)	50s
test-alloc (sigma_fun)	22s
test-minimal (sigma_fun)	14s
test-alloc (ecdsa_fun)	57s
test-nightly	49s
test-minimal (ecdsa_fun)	37s
test-alloc (schnorr_fun)	48s
test-minimal (schnorr_fun)	43s
	13m 45s

Provide feedback