[dbt-schema-builder] Upgrade python version to 3.12

[huniafatima-arbi]

Description:

Follow and complete all of the following steps for the issue to be marked as done.

• [x] Update the tox.ini, setup.py, setup.cfg, or pyproject.toml to remove Python 3.8 and add support for Python 3.12.
• [x] Ensure GitHub Actions workflows, including the CI matrix, are updated to reflect the supported Python versions (3.11, and 3.12).
• [x] Adjust any testing or build configurations to ensure compatibility with Python 3.12.
• [x] Remove references to Python versions earlier than 3.11 from all relevant configuration files.
• [x] Run all tests and verify they pass in the CI with the updated versions.
• [x] Add a CHANGELOG entry: “Dropped support for Python 3.8 and added support for Python 3.12.”
• [ ] Bump the package version and release a new version on GitHub & PyPI (where applicable).