GitHub Actions: fix permissions

.github/workflows/main.yml

@@ -9,7 +9,7 @@ jobs:
       run: |
         rm -rf ~/.conda/envs/miplearn-test
         yes | conda create --name miplearn-test python=3.8
-        (cd /opt/gurobi900/linux64 && sudo ~/.conda/envs/miplearn-test/bin/python setup.py install)
+        (cd /opt/gurobi900/linux64 && ~/.conda/envs/miplearn-test/bin/python setup.py install)
         ~/.conda/envs/miplearn-test/bin/pip install -r requirements.txt
         ~/.conda/envs/miplearn-test/bin/pytest