main.yml: Fix "pypy-3.9,urllib3<2" CI through recent Setuptools

Command "pip install codecov '.[tests]' 'urllib3<2'" was failing
with error:
> hpy 0.9.0 has requirement setuptools>=64.0, but you have
> setuptools 58.1.0.

.github/workflows/main.yml

@@ -49,7 +49,7 @@ jobs:
 
       - name: Install project dependencies
         run: |
-          pip install --upgrade pip
+          pip install --upgrade pip setuptools
           pip install codecov '.[tests]' '${{ matrix.urllib3-requirement }}'
           pip check