Add missing maturin install run step

Author: sk1p

.github/workflows/CI.yml

@@ -79,6 +79,7 @@ jobs:
     - uses: actions/setup-python@v6
       with:
         python-version: '3.13' 
+    - run: python3 -m pip install maturin
     - run: maturin develop -r
       working-directory: libertem_dectris
     - run: maturin develop -r