Make prereleased docs of pygame-ce be built

Author: andrewhong04

.github/workflows/build.yml

@@ -41,7 +41,7 @@ jobs:
       - name: Install pygame-ce
         run: |
           python -m pip install --upgrade pip
-          pip install pygame-ce
+          pip install pygame-ce --pre
       - name: Clone and move docs
         run: |
           python utils/generate_docs.py