update ubuntu version in test.yml

Author: Umesh Krishna

.github/workflows/test.yml

@@ -3,14 +3,14 @@ name: Test
 on:
   push:
     branches:
-      - master
+      - '**'
   pull_request:
     branches:
-      - master
+      - '**'
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11"]