Add ubuntu 20 to the tests

Author: Steven-Roberts

.github/workflows/tests.yml

@@ -8,7 +8,10 @@ on:
 
 jobs:
   octave:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-20.04, ubuntu-22.04]
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout Repo
         uses: actions/checkout@v4