chore: drop support for python 3.10 and django 3.2

[magajh]

Description:

This PR removes support for Django 3.2 and Python 3.10 from our plugin.

Rationale:

We have decided to drop support for these versions because none of the Open edX releases we support use Django 3.2 or Python 3.10. Therefore, maintaining compatibility with them is unnecessary.

For more context and information, please refer to AP-1490.

Changes:

• Updated the test workflow to remove Python 3.10 and Django 3.2 from the Python and Django matrix.
• Updated the tox.ini file to eliminate specifications for Python 3.10 and Django 3.2.
• Deleted the django32.txt file.
• Removed constraints that were only necessary for compatibility with Python 3.10 or Django 3.2.
• Upgraded the requirements using Python 3.8, which is the oldest version we now support.

How to Test:

• Ensure that all tests in the GitHub CI pipeline pass successfully.
• Verify that the pipeline no longer runs tests with Python 3.10 and Django 3.2.