CI: Update deprecated GH Actions runner image ubuntu-20.4 to 22.04.

Author: microbit-carlos

.github/workflows/build.yml

@@ -10,9 +10,13 @@ jobs:
   build-microbit-v2-samples:
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-13, windows-2019]
+        os: [ubuntu-22.04, macos-13, windows-2019]
         gcc: ['6-2016-q4', 'latest']  # Min version 6.2 as used in pext/yotta:latest docker image
         cmake: ['3.6.0', '']  # Empty string installs the latest CMake release
+        exclude:
+          # This old version of CMake doesn't run un Ubuntu 22.04
+          - os: ubuntu-22.04
+            cmake: '3.6.0'
       fail-fast: false
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.os }}, gcc ${{ matrix.gcc }}, cmake ${{ matrix.cmake || 'latest'}}

.github/workflows/on-release.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   cppcheck:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     name: Build against Ubuntu-20.04 for release assets
     steps:
       - uses: actions/checkout@v4