[Feature] Upgrade Dockerfile to 3.12

[dbeatty10]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

By the time Python 3.13 is released (around October 2024), we'll want to upgrade it to use Python 3.12 so that users are getting an up-to-date Python version that is a stable release still receiving bug fixes (and not merely security fixes).

Who will this benefit?

The Dockerfile in dbt-core is suitable for building dbt Docker images locally or using with CI/CD to automate populating a container registry.

Anything else?

There are a couple issues already in-flight to support Python 3.12:

• [Python 3.12] Support + test against python 3.12 in dbt-semantic-interfaces dbt-semantic-interfaces#257
• [CT-3325] [Tech Debt][Spike+] Test dbt-core with Python 3.12 #9007

Python 3.12 was released in October 2023: https://www.python.org/downloads/release/python-3120/

https://docs.getdbt.com/faqs/Core/install-python-compatibility

“New dbt minor versions will add support for new Python3 minor versions as soon as all dependencies can support it. In turn, dbt minor versions will drop support for old Python3 minor versions right before they reach end of life.”