build(docker): pin setuptools 70 (#724)

Pin `setuptools` to the maximum version of 70 to allow working on Ubuntu
20.04 LTS based environments. (New versions of `setuptools` are not
compatible.)

This commit is cherry-picked from
be6a3885f4f2e84ca77c7e09a89e5f2f06185452.

Author: Alputer

.github/workflows/ci.yml

@@ -1,5 +1,5 @@
 # This file is part of REANA.
-# Copyright (C) 2020, 2021, 2022, 2024 CERN.
+# Copyright (C) 2020, 2021, 2022, 2024, 2025 CERN.
 #
 # REANA is free software; you can redistribute it and/or modify it
 # under the terms of the MIT License; see LICENSE file for more details.
@@ -129,6 +129,7 @@ jobs:
 
       - name: Install Python dependencies
         run: |
+          pip install --upgrade pip 'setuptools<71' py
           pip install -e .[all]
 
       - name: Run Sphinx documentation with doctests
@@ -147,6 +148,7 @@ jobs:
 
       - name: Install Python dependencies
         run: |
+          pip install --upgrade pip 'setuptools<71' py
           pip install twine wheel
           pip install -e .[all]