ci: remove unneeded setuptools install

I don't think it's needed.

Author: bluetech

.github/workflows/prepare-release-pr.yml

@@ -41,7 +41,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install --upgrade setuptools tox
+        pip install --upgrade tox
 
     - name: Prepare release PR (minor/patch release)
       if: github.event.inputs.major == 'no'