Fix GH Action Docker build error

[geekygirlsarah]

What GitHub issue does this PR apply to?

N/A

What changed and why?

Fix the Docker build by setting image to Python 3.12-slim (stable) rather than 3-slim (3.14 beta) which doesn't have a psychopg2-binary package for it. also add in libpq-dev library to hopefully help fix issues.

AI bots used in the process of making this PR

Jetbrains Junie

When I try to build the Docker container using a GitHub Action to verify it works, sometimes it fails and sometimes it works. It's related to psycopg2-binary but I haven't been able to figure out what is actually wrong to prevent it from working on GitHub when it works locally. Here's the output:

[pasted error]

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Checklist

• I claimed any associated issue(s) and they are not someone else's
• I have looked at documentation to ensure I made any revisions correctly
• I tested my changes locally to ensure they work
• For language files, I have validated the edited files are valid JSON and data shows up correctly
• For website code edits, I have added or edited any appropriate unit tests for my changes
• If I used artificial intelligence (AI), I have reviewed the suggested changes and ensured they work correctly

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