Update to Ubuntu 22.04 in CI

Author: argilo

.github/workflows/ci.yml

@@ -5,10 +5,10 @@ on: [push, pull_request]
 jobs:
   tests:
     name: "Python ${{ matrix.python-version }}"
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
     steps:
       - name: Install dependencies
         run: sudo apt-get install -y gcc-avr avr-libc simulavr