build: Switch to ubuntu-latest for builds

This code does not have any dependencies that are specific to any specific
version of ubuntu.  So instead of testing on a specific version and then needing
to do work to keep the versions up-to-date, we switch to the ubuntu-latest
target which should be sufficient for testing purposes.

This work is being done as a part of openedx/platform-roadmap#377

closes #281

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
  strategy:
  fail-fast: false
  matrix:
- os: [ubuntu-20.04]
+ os: [ubuntu-latest]
  python-version: [3.8, 3.11, 3.12]
  test-target: [test, quality]
 

.github/workflows/pypi-publish.yml

@@ -7,7 +7,7 @@ on:
 jobs:
 
  push:
- runs-on: ubuntu-20.04
+ runs-on: ubuntu-latest
 
  steps:
  - name: Checkout