ci: fix typo--requirements

.github/workflows/sphinx.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r ./requirement/requirements.txt
+          pip install -r ./requirements/requirements.txt
       - name: Build docs
         run: |
           cd docs && make html