CI: Update runner to use ubuntu-20.04.

Signed-off-by: Damien George <[email protected]>

Author: dpgeorge

.github/workflows/build.yml

@@ -10,20 +10,18 @@ jobs:
   build:
     strategy:
       matrix:
-        os: [ubuntu-18.04]
+        os: [ubuntu-20.04]
       fail-fast: false
     runs-on: ${{ matrix.os }}
     name: build.py ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: true
       - name: Install toolchain (Ubuntu)
         if: runner.os == 'Linux'
         run: |
-          sudo add-apt-repository -y ppa:team-gcc-arm-embedded/ppa
-          sudo apt-get update -qq
-          sudo apt-get install -y gcc-arm-embedded
+          sudo apt-get install -y gcc-arm-none-eabi libnewlib-arm-none-eabi
           sudo apt-get install -y cmake
       - name: Check Versions
         run: |
@@ -35,7 +33,7 @@ jobs:
           cd src
           make -j2
       - name: Upload hex file
-        uses: actions/upload-artifact@v1
+        uses: actions/upload-artifact@v3
         with:
           name: MICROBIT-MICROPYTHON-${{ github.sha }}.hex
           path: src/MICROBIT.hex