Upgrade to Python 3.9.18 and fix CI compatibility issues

[mmmavis]

Related to Jira ticket: https://mozilla-hub.atlassian.net/browse/TP1-2209?atlOrigin=eyJpIjoiNzA5MDI1MjE4OTljNDNlOTlkMTU1ZDgzZTU5MDg0NzkiLCJwIjoiaiJ9

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This PR resolves the issues we got from Heroku

-----> Building on the Heroku-24 stack
-----> Using buildpack: heroku/python
-----> Python app detected
-----> Using Python 3.7.8 specified in runtime.txt
! Error: The requested Python version has reached end-of-life.
!
! Python 3.7 has reached its upstream end-of-life, and is
! therefore no longer receiving security updates:
! https://devguide.python.org/versions/#supported-versions
!
! As such, it's no longer supported by this buildpack:
! https://devcenter.heroku.com/articles/python-support#supported-python-versions
!
! Please upgrade to at least Python 3.9 by changing the
! version in your runtime.txt file.
! Push rejected, failed to compile Python app.
! Push failed

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To test:

• follow the Setup instructions
• make sure you can access the app. e.g.,
  • go to http://localhost:8000/api/pulse/v2/entries/ to see if everything loads
  • you are able to log in to admin dashbaord http://localhost:8000/admin/

[danielfmiranda]

Thanks @mmmavis! LGTM 👍