ci fixups

- Coincurve's MacOS dependencies may be necessary if it's falling back
  to building from source.
- setuptools needs to be installed explicitly, pytest doesn't
- requirements.txt already gets installed by setup.py
- Install test requirements at testing step

.github/workflows/python-package.yml

@@ -24,14 +24,18 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
-    - name: Installation (deps and package)
+    - name: Install pip and setuptools
       run: |
         python -m pip install --upgrade pip
-        pip install pytest
-        pip install -r requirements.txt -r tests/requirements.txt
-        python setup.py install
+        pip install setuptools
+    - name: Install coincurve wheels for MacOS
+      if: matrix.os == 'macos-latest' || matrix.os == 'macos-13'
+      run: pip install -r requirements.txt
+    - name: Install from source
+      run: python setup.py install
     - name: Test with pytest
       run: |
+        pip install -r tests/requirements.txt
         pytest -vvv
 
   linter: