Explicitly install dependencies

It is very buggy if we let setuptools do it for some reason, so have
this as an explicit step instead.

.github/workflows/test.yml

@@ -21,10 +21,13 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Install dependencies
+      - name: Update pip and setuptools
         run: |
           python -m pip install --upgrade pip
           python -m pip install setuptools
+      - name: Install dependencies
+        run: |
+          python -m pip install -e .
           python -m pip install -r test-requirements.txt
       - name: Install old numpy
         run: |