Switch CI from ubuntu-latest to ubuntu-20.04 to avoid problems with ansible-test from ansible-core 2.12, 2.13, 2.14. (#138)

.github/workflows/ansible-test.yml

@@ -33,7 +33,7 @@ jobs:
           - stable-2.13
           - stable-2.14
           - devel
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Perform sanity testing
         uses: ansible-community/ansible-test-gh-action@release/v1
@@ -46,7 +46,7 @@ jobs:
             git clone --depth=1 --single-branch https://github.com/ansible-collections/ansible.utils.git ../../ansible/utils
 
   units:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: Units (Ⓐ${{ matrix.ansible }})
     strategy:
       # As soon as the first unit test fails, cancel the others to free up the CI queue
@@ -75,7 +75,7 @@ jobs:
             git clone --depth=1 --single-branch https://github.com/ansible-collections/ansible.utils.git ../../ansible/utils
 
   integration:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: I (Ⓐ${{ matrix.ansible }}+py${{ matrix.python }})
     strategy:
       fail-fast: false