The substitution patch used to point nextcord to the installed location
of libopus in nix's store was incorrectly formatted:
* `@opus@` was used while default.nix attempted to substitute instances of
`@libopus@`.
* `ctypes.util.find_library(<library_name>)` will return a path to a
library. If we already have the path (provided by the substitution),
then `find_library` is not necessary to call (nor will it produce the
desired result).
d6673a51bc