[FIX] fix build docs workflow

Author: bnbong

.github/workflows/build-docs.yml

@@ -33,18 +33,9 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12.4"
-      - uses: pdm-project/setup-pdm@v4
       - name: Install docs dependencies
         run: |
-          echo "Attempting to install docs dependencies with PDM..."
-          if pdm install --group docs --no-default; then
-            echo "PDM install succeeded"
-          else
-            echo "PDM install failed or PDM not available, falling back to requirements-docs.txt"
-            echo "Installing dependencies via pip..."
             pip install -r requirements-docs.txt
-            echo "Fallback installation completed"
-          fi
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
       - uses: actions/cache@v4
         with: