Remove hard-coded python version in Tools/pixi-packages #148858

[isuruf]

Feature or enhancement

Proposal:

Tools/pixi-packages/default/variants.yaml has the following

variant:
  - default
abi_tag:
  - cp315
version:
  - 3.15

We can remove the hard-coding of 3.15

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

Suggested in #148859 (review)

Linked PRs

• gh-148887: Remove version hardcoding in Tools/pixi-packages #148890