Install requirements in one pass and cache pip

Author: matt-graham

.github/workflows/tests.yml

@@ -32,12 +32,12 @@ jobs:
       uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
+        cache: pip
 
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install -r requirements/requirements-tests.txt
-        pip install -r requirements/requirements-core.txt
+        pip install -r requirements/requirements-core.txt -r requirements/requirements-tests.txt
         pip install .
     
     - name: Run tests