Update runner version for Debian package (#719)

Routine update to switch from depreciated runner to a current one.

Author: daniel-123

.github/workflows/build.yml

@@ -139,7 +139,7 @@ jobs:
 
   deb:
     name: Build Debian package
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v2