remove testers

Author: PhilipVinc

.github/workflows/system.yml

@@ -34,14 +34,6 @@ jobs:
             architecture: x64
             python-version: '3.9'
             julia-version: '1'
-          - os: ubuntu-latest
-            architecture: x64
-            python-version: '3.x'
-            julia-version: '1.5'
-          - os: ubuntu-latest
-            architecture: x64
-            python-version: '3.x'
-            julia-version: '1.4'
           # Test Python 2.7 only with a few combinations (TODO: drop 2.7).
           # Note that it does not work in macOS:
           - os: ubuntu-latest