Install poetry and flake before pushing the SDK

Author: vicentepinto98

.github/workflows/sdk-pr.yaml

@@ -64,4 +64,7 @@ jobs:
           GH_REPO: "stackitcloud/stackit-sdk-python"
           GH_TOKEN: ${{ secrets.SDK_PR_TOKEN }}
         run: |
+          pip install poetry
+          poetry config virtualenvs.create false
+          pip install flake8
           scripts/sdk-create-pr.sh "generator-bot-${{ github.run_id }}" "Generated from GitHub run [${{ github.run_id }}](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})" "git@github.com:stackitcloud/stackit-sdk-python.git" "python"