Pin ubuntu to 20.04 for tests.

Author: gkhaburzaniya-onelogin

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-20.04, macos-latest]
         ruby-version: [2.1.9, 2.2.10, 2.3.8, 2.4.6, 2.5.8, 2.6.6, 2.7.2, 3.0.1, '3.1', jruby-9.1.17.0, jruby-9.2.17.0, truffleruby]
     runs-on: ${{ matrix.os }}
     steps: