Fix Cython tests on Python 3.12 (#1759)

Our "test from PyPI" workflow was failing with Python 3.12 because it
exercised the Cython tests, which use `cython.inline`, and
`cython.inline` in turn uses `distutils`, which no longer exists in the
Python 3.12 standard library.

As a temporary workaround, this PR adds `setuptools` to the list of
packages installed into the test environment; `setuptools` provides a
shim for `distutils`.

I'd guess that at some point in the reasonably near future the
dependence of Cython on `distutils` will be fixed.

Closely related upstream issue:
cython/cython#5751

.github/workflows/test-from-pypi.yml

@@ -48,11 +48,11 @@ jobs:
         allow-prereleases: true
     - name: Install test dependencies and Traits from PyPI sdist (no PySide6)
       run: |
-        python -m pip install --no-binary traits Cython numpy Sphinx traits traitsui
+        python -m pip install --no-binary traits Cython numpy setuptools Sphinx traits traitsui
       if: matrix.python-version == '3.12' || matrix.python-architecture == 'x86'
     - name: Install test dependencies and Traits from PyPI sdist (PySide6)
       run: |
-        python -m pip install --no-binary traits Cython numpy PySide6 Sphinx traits traitsui
+        python -m pip install --no-binary traits Cython numpy PySide6 setuptools Sphinx traits traitsui
       if: matrix.python-version != '3.12' && matrix.python-architecture != 'x86'
     - name: Create clean test directory
       run: |
@@ -100,11 +100,11 @@ jobs:
         allow-prereleases: true
     - name: Install test dependencies and Traits from PyPI wheel (no PySide6)
       run: |
-        python -m pip install --only-binary traits Cython numpy Sphinx traits traitsui
+        python -m pip install --only-binary traits Cython numpy setuptools Sphinx traits traitsui
       if: matrix.python-version == '3.12' || matrix.python-architecture == 'x86'
     - name: Install test dependencies and Traits from PyPI wheel (PySide6)
       run: |
-        python -m pip install --only-binary traits Cython numpy PySide6 Sphinx traits traitsui
+        python -m pip install --only-binary traits Cython numpy PySide6 setuptools Sphinx traits traitsui
       if: matrix.python-version != '3.12' && matrix.python-architecture != 'x86'
     - name: Create clean test directory
       run: |