Make CI use a dummy password hasher for all tests (#22983)

During the recent hash algorithm change it became clear that the choice
of password hash algorithm plays a role in the time taken for CI to run.

Therefore as attempt to improve CI we should consider using a dummy
hashing algorithm instead of a real hashing algorithm.

This PR creates a dummy algorithm which is then set as the default
hashing algorithm during tests that use the fixtures. This hopefully
will cause a reduction in the time it takes for CI to run.

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/auth/password/hash/scrypt.go

@@ -13,7 +13,7 @@ import (
 )
 
 func init() {
-	Register("scrypt", NewScryptHasher)
+	MustRegister("scrypt", NewScryptHasher)
 }
 
 // ScryptHasher implements PasswordHasher