[CI] Address problems with cygwin (pypa#4832, pypa/distutils#328)

Author: abravalheri

.github/workflows/main.yml

@@ -112,14 +112,19 @@ jobs:
             python${{ matrix.python }},
             python${{ matrix.python }}-devel,
             python${{ matrix.python }}-pytest,
-            python${{ matrix.python }}-tox,
+            python${{ matrix.python }}-pip,
             gcc-core,
             gcc-g++,
             ncompress
             git
+      - name: Install tox using pip
+        shell: C:\cygwin\bin\env.exe CYGWIN_NOWINPATH=1 CHERE_INVOKING=1 C:\cygwin\bin\bash.exe -leo pipefail -o igncr {0}
+        run: |
+          # Workaround for https://github.com/pypa/setuptools/issues/4831
+          python -m pip install tox
       - name: Run tests
         shell: C:\cygwin\bin\env.exe CYGWIN_NOWINPATH=1 CHERE_INVOKING=1 C:\cygwin\bin\bash.exe -leo pipefail -o igncr {0}
-        run: tox
+        run: python -m tox
 
   test_msys2_mingw:
     strategy: