Remove setup-python actions

We installed Python in a container, so the action will not work.

.github/workflows/build.yml

@@ -41,10 +41,6 @@ jobs:
         with:
           path: ~/.cache/pip
           key: python${{ env.python_version }}-${{ hashFiles('**/poetry.lock') }}-41
-      - name: Set up Python ${{ env.python_version }}
-        uses: actions/setup-python@f677139bbe7f9c59b41e40162b753c062f5d49a3 # v5.2.0
-        with:
-          python-version: ${{ env.python_version }}
       - name: Install Poetry
         run: |
           python${{ env.python_version }} -m ensurepip