Build Docker images with Python 3.12

[frebib]

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
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• Pull request includes a sign off
• Code style is correct
  (run the linters)

[frebib]

I'm not entirely sure if there's a reason that Synapse hasn't been updated yet, but python 3.12 has been out for a while, and I've been running this for a while on my homeserver with seemingly no issues

[clokep]

I'm not entirely sure if there's a reason that Synapse hasn't been updated yet

I think just being a bit conservative to see if there's any major bugs in Python 3.12.0. So, no real reason.

[clokep]

We had a conversation about this at https://matrix.to/#/!vcyiEtMVHIhWXcJAfl:sw1v.org/$jKrddG8OwjueQLieMigclhpg6zFltijWQUPE2xPDsSQ?via=matrix.org&via=element.io&via=envs.net -- it seems that we'd like to wait a bit more for this since we're still seeing Python 3.12 support being added to packages. We previously always ran a version behind on Python to be conservative, but broke this in Python 3.11 (since it has a significant performance improvements).

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Out of curiosity -- is there anything driving this? Do you see better performance when building with 3.12, or just interested in running the latest?