build fails pip update of pip setuptools wheel

Full log and script attached, however, here is the relevant part:

+ snapcraftctl build
+ python3 -m venv /home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install
+ SNAPCRAFT_PYTHON_VENV_INTERP_PATH=/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/bin/python3
+ pip install -U pip setuptools wheel
Collecting pip
  Using cached pip-23.1.2-py3-none-any.whl (2.1 MB)
Collecting setuptools
  Using cached setuptools-67.7.2-py3-none-any.whl (1.1 MB)
Collecting wheel
  Using cached wheel-0.40.0-py3-none-any.whl (64 kB)
Installing collected packages: pip, setuptools, wheel
  Attempting uninstall: pip
    Found existing installation: pip 20.0.2
    Uninstalling pip-20.0.2:
      Successfully uninstalled pip-20.0.2
  Attempting uninstall: setuptools
    Found existing installation: setuptools 45.2.0
    Uninstalling setuptools-45.2.0:
      Successfully uninstalled setuptools-45.2.0
  Attempting uninstall: wheel
    Found existing installation: wheel 0.34.2
    Uninstalling wheel-0.34.2:
      Successfully uninstalled wheel-0.34.2
Successfully installed pip-23.1.2 setuptools-67.7.2 wheel-0.40.0
+ pip install -U -r requirements.txt
Traceback (most recent call last):
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 629, in _build_master
    ws.require(__requires__)
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 966, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 827, in resolve
    dist = self._resolve_dist(
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 873, in _resolve_dist
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.VersionConflict: (pip 23.1.2 (/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages), Requirement.parse('pip==20.0.2'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/usr/bin/pip", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3327, in <module>
    def _initialize_master_working_set():
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3301, in _call_aside
    f(*args, **kwargs)
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 3339, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 631, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 644, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 827, in resolve
    dist = self._resolve_dist(
  File "/home/ken/workspace/duplicity-main/build/duplicity-1.2.4.dev2/parts/duplicity/install/lib/python3.8/site-packages/pkg_resources/__init__.py", line 868, in _resolve_dist
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pip==20.0.2' distribution was not found and is required by the application
Failed to build 'duplicity'.

It tries to upgrade to the newest version in the venv, then fails because pkg-resources installed from apt wants the ancient version it uses.