Require Znumtheory before using it

[andres-erbsen]

For rocq-prover/stdlib#136

[andres-erbsen]

  Error response from daemon: No such image: mathcomp/mathcomp-dev:coq-dev
  Error response from daemon: manifest for mathcomp/mathcomp-dev:coq-dev not found: manifest unknown: manifest unknown

[andres-erbsen]

Dear maintainers,

Do you consider this PR acceptable enough to merge it so that the related stdlib change can progress?

Thanks!

[pi8027]

We should fix CI before merging this, but I don't have time to do it right now. Ping @math-comp/core

[andres-erbsen]

Ack. Looks like the ping did not highlight, so maybe it didn't work.

(Also note that the change itself is trivial -- unless Znumtheory.something used to refer to something other than stdlib Znumtheory, just on the versions that the CI is broken, this change is a no-op.)

[CohenCyril]

CI fixed but for one CI target where the docker image is still work in progress (AFAIU). LGTM. Let's merge!

[CohenCyril]

Ack. Looks like the ping did not highlight, so maybe it didn't work.

The ping did work but I guess most of the team was on vacation or something...

[pi8027]

Thanks!