Don't use Sphinx 4 for the moment (#457)

* Don't use Sphinx 4 for the moment

* docs, not doc

.github/workflows/build-docs.yml

@@ -26,8 +26,7 @@ jobs:
     - name: Install dependencies and local packages
       run: |
         python -m pip install --upgrade pip setuptools wheel
-        python -m pip install sphinx enthought-sphinx-theme
-        python -m pip install .
+        python -m pip install .[docs]
     - name: Build HTML documentation with Sphinx
       run: |
         cd docs

.github/workflows/test-docs.yml

@@ -22,12 +22,11 @@ jobs:
     - name: Install necessary Python packages
       run: |
         python -m pip install --upgrade pip setuptools wheel
-        python -m pip install sphinx enthought-sphinx-theme
     - name: Check out the PR branch
       uses: actions/checkout@v2
-    - name: Install local package
+    - name: Install local package and documentation dependencies
       run: |
-        python -m pip install .
+        python -m pip install .[docs]
     - name: Build HTML documentation
       run: |
         cd docs

setup.py

@@ -49,7 +49,7 @@ def get_long_description():
     extras_require={
         "pyqt5": ["pyqt5"],
         "pyside2": ["pyside2"],
-        "docs": ["enthought-sphinx-theme", "sphinx>=3.5"],
+        "docs": ["enthought-sphinx-theme", "sphinx>=3.5,<4"],
     },
     packages=find_packages(exclude=["ci"]),
     classifiers=[