Drop python 3.8 & update Jax to 0.4.14

[rmoyard]

Description of the Change:

• Remove python 3.8
• Update Jax version on the CI checks.

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[rmoyard]

[sc-37949]

[codecov]

Codecov Report

Merging #4453 (893d43e) into master (5495875) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4453   +/-   ##
=======================================
  Coverage   99.77%   99.77%           
=======================================
  Files         371      371           
  Lines       33910    33910           
=======================================
  Hits        33834    33834           
  Misses         76       76           

[mudit2812]

Thanks Romain! Could you open a PR on the pennylane.ai-react repo with the update as well? You can see an example here https://github.com/XanaduAI/pennylane.ai-react/pull/371

[mlxd]

Hey @rmoyard, since the docs-builder also installs PennyLane under 3.8, can you update the python version there too to 3.9?

Once this goes through I'll update the expected CI requirements in the repo

[mlxd]

Thanks @rmoyard !