Change Ubuntu version in CI workflow (#222)

* Change Ubuntu version in CI workflow

Updated the workflow to use Ubuntu 22.04 instead of 20.04.

* Exclude Python 3.6 on ubuntu-22.04 in CI workflow

Added exclusion for Python 3.6 on ubuntu-22.04 in workflow.

Author: okigan

.github/workflows/pythonapp.yml

@@ -6,11 +6,13 @@ jobs:
   build:
     strategy:
       matrix:
-        runs-on: [ubuntu-20.04, ubuntu-latest, macOS-latest]
+        runs-on: [ubuntu-22.04, ubuntu-latest, macOS-latest]
         python-version: [ '3.6', '3.8', '3.9', '3.11']
         exclude:
           - runs-on: ubuntu-latest
             python-version: '3.6'
+          - runs-on: ubuntu-22.04
+            python-version: '3.6'
           - runs-on: macOS-latest
             python-version: '3.6'
       fail-fast: false