[ci] Fix arm build

Author: serge-sans-paille

.github/workflows/cross.yml

@@ -5,7 +5,7 @@ concurrency:
   cancel-in-progress: true
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: '${{ matrix.target.arch }}, ${{ matrix.sys.compiler }} ${{ matrix.sys.version }}'
     strategy:
       matrix:
@@ -14,7 +14,7 @@ jobs:
           - { platform: 'arm',     arch: 'armv7-a', dir: 'arm-linux-gnueabihf', flags: '-mfpu=vfpv3-d16', full: 'OFF' } # no neon
           - { platform: 'aarch64', arch: 'armv8-a', dir: 'aarch64-linux-gnu', flags: '', full: 'ON' }
         sys:
-          - { compiler: 'gcc',   version: '8' }
+          - { compiler: 'gcc',   version: '9' }
           - { compiler: 'clang', version: 'latest' }
     steps:
     - name: Setup compiler