ICC CI: Downgrade pytest

pytest 6 does not capture the `discard_as_unraisable` stderr and
just writes a warning with its content instead.

Author: ax3l

.github/workflows/ci.yml

@@ -416,7 +416,7 @@ jobs:
       run: |
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
         python3 -m pip install --upgrade pip
-        python3 -m pip install --upgrade pytest
+        python3 -m pip install --upgrade pytest==5.4.3
 
     - name: Configure
       shell: bash