CI: Pin Cygwin setuptools<60 and avoid problem upgrades

setuptools>=60 runs into python-pillow/Pillow#6216 and pypa/setuptools#3304.

NumPy==1.21.* has intermittent segfaults due to SIMD attempts on unaligned memory.

kiwisolver, numpy, and pillow have problems installing, so just verify that they are present, don't try to upgrade them.

.github/workflows/tests.yml

@@ -157,11 +157,11 @@ jobs:
         run: |
           # Upgrade pip and setuptools and wheel to get as clean an install as
           # possible.
-          python -m pip install --upgrade pip 'setuptools<60' wheel
+          python -m pip install --upgrade pip setuptools wheel
 
           # Install dependencies from PyPI.
           python -m pip install --upgrade $PRE \
-            cycler fonttools kiwisolver 'numpy!=1.21.*' packaging pillow pyparsing \
+            cycler fonttools kiwisolver numpy packaging pillow pyparsing \
             python-dateutil setuptools-scm \
             -r requirements/testing/all.txt \
             ${{ matrix.extra-requirements }}
@@ -370,9 +370,11 @@ jobs:
       - name: Install Python dependencies
         shell: bash.exe -eo pipefail -o igncr "{0}"
         run: |
-          python -m pip install --upgrade setuptools wheel
+          python -m pip install --upgrade 'setuptools<60' wheel
+          python -m pip install kiwisolver 'numpy!=1.21.*' pillow
+          grep -v -F -e psutil requirements/testing/all.txt >requirements_test.txt
           python -m pip install --upgrade cycler fonttools kiwisolver numpy packaging pillow pyparsing \
-              python-dateutil setuptools-scm -r requirements/testing/all.txt sphinx
+              python-dateutil setuptools-scm -r requirements_test.txt sphinx
           python -m pip install --upgrade pycairo 'cairocffi>=0.8' PyGObject &&
              python -c 'import gi; gi.require_version("Gtk", "3.0"); from gi.repository import Gtk' &&
              echo 'PyGObject is available' ||