CI: Run Python 3.5 on ubuntu-20.04

Author: remram44

.github/workflows/test.yml

@@ -8,13 +8,16 @@ jobs:
   build:
     strategy:
       matrix:
+        os: [ubuntu-latest]
         python-version:
           - "2.7"
-          - "3.5"
           - "3.7"
           - "3.8"
           - "3.9"
-    runs-on: ubuntu-latest
+        include:
+          - os: ubuntu-20.04
+            python: "3.5"
+    runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v3
     - uses: actions/setup-python@v4