Update Python version to 3.9.5

The minimal updates here were to update pygit2 and pip-tools.

However, prospector is currently broken as well, so the full code style
checks currently will not pass. This is not trivial to fix:

  - Currently, pylint returns errors from some of the mypy annotations
  - Upgrading pylint/astroid to the newest version fixes those errors,
    but breaks prospector
  - There is no newer release of prospector

I'm not totally sure how I want to fix this, I may need to fork
prospector.

ansible/roles/python/tasks/main.yml

@@ -10,8 +10,8 @@
     - name: Download Python source code
       get_url:
         dest: /tmp/python.tar.gz
-        url: https://www.python.org/ftp/python/3.8.10/Python-3.8.10.tgz
-        checksum: sha256:b37ac74d2cbad2590e7cd0dd2b3826c29afe89a734090a87bf8c03c45066cb65
+        url: https://www.python.org/ftp/python/{{ python_full_version }}/Python-{{ python_full_version }}.tgz
+        checksum: sha256:e0fbd5b6e1ee242524430dee3c91baf4cbbaba4a72dd1674b90fda87b713c7ab
 
     - name: Create temp directory to extract Python to
       file: