Test Ubuntu wheel on 20.04 (#6205)

Author: ssheorey

.github/workflows/ubuntu-wheel.yml

@@ -109,7 +109,7 @@ jobs:
 
   test-wheel-cpu:
     name: Test wheel CPU
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     needs: [build-wheel]
     strategy:
       fail-fast: false