Use more recent Mamba

Author: jonashaag

ci/setup_env.sh

@@ -52,7 +52,7 @@ echo "update conda"
 conda config --set ssl_verify false
 conda config --set quiet true --set always_yes true --set changeps1 false
 # TODO: GH#44980 https://github.com/pypa/setuptools/issues/2941
-conda install -y -c conda-forge -n base mamba pip 'setuptools<60'
+conda install -y -c conda-forge -n base 'mamba>=0.21.2' pip 'setuptools<60'
 
 echo "conda info -a"
 conda info -a