GitHub Actions: Build Raspbian on Ubuntu 22.04

Raspbian builds were running on Ubuntu 20.04 but with qemu-user-static from Ubuntu 21.10 (impish) due to need for newer features. However, the impish package repos are no longer available as that version reached its EOL. ubuntu-latest still refers to 20.04 on GitHub Actions but 22.04 is already available when explicitly specified. This commit switches the build over to that version and removes the workaround.

.github/workflows/raspbian.yml

@@ -18,7 +18,7 @@ jobs:
           - buster
           - bullseye
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04 # revert back to ubuntu-latest once that is 22.04 or later
 
     steps:
       - name: Cancel previous jobs for the same PR
@@ -34,10 +34,6 @@ jobs:
       - name: qemu-user-static
         run: |
           set -exo pipefail
-          . /etc/os-release
-          if [ "$VERSION_ID" = 20.04 ]; then
-            sudo perl -pi -e s/focal/impish/g /etc/apt/sources.list
-          fi
           sudo apt-get update
           DEBIAN_FRONTEND=noninteractive sudo apt-get install -y qemu-user-static