fix(ci): run .github/workflows/workflow.yml on ubuntu-20.04 (#535)

Author: mayeut

.github/workflows/workflow.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ${{ matrix.operating-system }}
     strategy:
       matrix:
-        operating-system: [ubuntu-latest, windows-latest]
+        operating-system: [ubuntu-20.04, windows-latest]
     steps:
     - name: Checkout
       uses: actions/checkout@v3
@@ -68,7 +68,7 @@ jobs:
         python-version: 3.8
     - name: Verify 3.8
       run: python __tests__/verify-python.py 3.8
-    
+
     - name: Run with setup-python 3.7.5
       uses: ./
       with: