try catch the latest compatible version

Author: Davide Laghi

.github/workflows/pytest.yml

@@ -66,7 +66,7 @@ jobs:
       - name: Install openmc (legacy)
         if: runner.os == 'Linux' && matrix.python-version == '3.11'
         run: |
-          pip install git+https://github.com/openmc-dev/openmc.git@v0.15.3#egg=openmc
+          pip install git+https://github.com/openmc-dev/openmc.git@3b5ac08bfb754ef93ff3db12fcda2ecbd0dbe464
       
       - name: Install openmc
         if: runner.os == 'Linux' && matrix.python-version != '3.10' && matrix.python-version != '3.11'