Chore: update to Python 3.12

[lalver1]

Closes #51

Tested Benefits locally by:

• Built a docker-python-web image locally using this branch
• Built an eligibility-server image locally using the local docker-python-web image built from this branch
• Built Benefits (both the client service and the dev container) from the local docker-python-web image

• Tested the Benefits app (a login.gov and an agency card flow). Everything looked ok.

Follow-up

Update .github/workflows/.python-version and tool.black.target-versionin pyproject.toml to 3.12 in

• eligibility-server
• benefits

[thekaveman]

👍 nice

Can you also take a follow-up to update the littlepay version please

• https://github.com/cal-itp/littlepay/blob/main/.devcontainer/Dockerfile#L1
• https://github.com/cal-itp/littlepay/blob/main/.github/workflows/release.yml#L34

And eligibility-api:

• https://github.com/cal-itp/eligibility-api/blob/main/.devcontainer/Dockerfile#L1
• https://github.com/cal-itp/eligibility-api/blob/main/.github/workflows/.python-version

These aren't directly related, but libraries used by benefits and we should just make sure everything is on the same version.