fix/ci(tests): attempt to fix windows pip installation

Author: amyheather

.github/workflows/tests.yaml

@@ -45,7 +45,7 @@ jobs:
         with:
           python-version: '3.13'
           cache: 'pip'
-      - run: pip install -r requirements.txt
+      - run: python -m pip install -r requirements.txt
 
       - name: Run tests
         run: pytest