CI: avoid virtualenv v21, hatch doesn't like it.

Author: PMeira

ci/build_linux.sh

@@ -3,5 +3,6 @@ export PATH=/opt/python/cp39-cp39/bin/:$PATH
 
 cd dss_python
 python3 -m pip install --upgrade pip wheel hatch
+python3 -m pip install 'virtualenv<21'
 python3 -m hatch build "../artifacts"
 cd ..

ci/build_wheel.sh

@@ -1,5 +1,5 @@
 mkdir -p artifacts
 cd dss_python
 $PYTHON -m pip install --upgrade pip wheel hatch
-$PYTHON -m pip install cffi numpy pytest
+$PYTHON -m pip install cffi numpy pytest 'virtualenv<21' 
 $PYTHON -m hatch build "$ARTIFACTS_FOLDER"