Use correct python version in environment

Author: alejoe91

.github/workflows/io-test.yml

@@ -74,6 +74,7 @@ jobs:
         # restore-key hits should result in `cache-hit` == 'false'
         if: steps.cache-conda-env.outputs.cache-hit != 'true'
         run: |
+          conda install python=${{ matrix.python-version }} --yes
           conda env update --name neo-test-env --file environment_testing.yml --prune
 
       - name: Configure git