add migration for pytorch 2.9

[h-vetinari]

Follow-up to conda-forge/pytorch-cpu-feedstock#448

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

[hmaarrfk]

hm the commit message is mesleading in the yaml

[weiji14]

Copy-paste typo...

Suggested change

	commit_message: Rebuild for pytorch 2.8
	commit_message: Rebuild for pytorch 2.9

[h-vetinari]

hm the commit message is misleading in the yaml

yes, sorry about that. It got fixed in #7997

[hmaarrfk]

I didn’t know if we could just edit things like that. Thanks.

[h-vetinari]

I didn’t know if we could just edit things like that. Thanks.

There are some sensitive things, but the commit message is not among them. We shouldn't change:

• migrator filename (determines the whole migration)
• migrator timestamp (determines whether migrator files in feedstock count as "applied")
• substantially change pins while migration is running

There's some exceptions where the third point can be justified (e.g. to couple two migrations that have log-jammed), but otherwise, the commit message, excxlude: etc. can easily be fixed after the fact, and will be picked up as soon as the new pinning makes it into the lockfile of https://github.com/regro/cf-scripts/