actions: use newest pytest-asyncio for ubuntu 20

Author: lonvia

.github/workflows/ci-tests.yml

@@ -93,7 +93,7 @@ jobs:
               if: matrix.flavour != 'oldstuff'
 
             - name: Install newer pytest-asyncio
-              run: pip3 install -U pytest-asyncio==0.21.1
+              run: pip3 install -U pytest-asyncio
               if: matrix.flavour == 'ubuntu-20'
 
             - name: Install test prerequsites (from pip for Ubuntu 18)