Update the linter to run on a valid github-hosted-runner

 - ubuntu-20.04 has been deprecated
  - using ubuntu-latest for robustness

Author: michelle-yooh

.github/workflows/CPUTests.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-latest]
         python-version: ['3.10']
     steps:
     - uses: actions/checkout@v3