Remove allow-prereleases: true flag

Author: schloerke

.github/py-shiny/setup/action.yaml

@@ -12,7 +12,6 @@ runs:
         uses: actions/setup-python@v5
         with:
           python-version: ${{ inputs.python-version }}
-          allow-prereleases: true
 
       - name: Upgrade `pip`
         shell: bash