Use a venv for Python dependency tooling

The version of Python installed as a system package is marked as
externally managed per PEP 668 and the pipenv Python package is not
available as a system package. Therefore we need to create a venv for
the Python packages we use for setup (pip, setuptools, wheel, and
pipenv).

Dockerfile

@@ -32,20 +32,23 @@ RUN apk --no-cache add \
   python3=3.12.8-r1
 
 ###
-# Install the specified versions of pip, setuptools, and wheel into the system
-# Python environment; install the specified version of pipenv into the system Python
-# environment; set up a Python virtual environment (venv); and install the specified
-# versions of pip, setuptools, and wheel into the venv.
+# Create a Python virtual environment (venv) for setup (due to PEP 668); install the
+# specified versions of pip, setuptools, and wheel into the setup venv; install the
+# specified version of pipenv into the setup venv; create the image dependency venv;
+# and install the specified versions of pip, setuptools, and wheel into the dependency
+# venv.
 #
 # Note that we use the --no-cache-dir flag to avoid writing to a local
 # cache.  This results in a smaller final image, at the cost of
 # slightly longer install times.
 ###
-RUN python3 -m pip install --no-cache-dir --upgrade \
+RUN python3 -m venv --system-site-packages /usr/local \
+    # Ensure the core Python packages are installed in the virtual environment
+    && /usr/local/bin/python3 -m pip install --no-cache-dir --upgrade \
         pip==${PYTHON_PIP_VERSION} \
         setuptools==${PYTHON_SETUPTOOLS_VERSION} \
         wheel==${PYTHON_WHEEL_VERSION} \
-    && python3 -m pip install --no-cache-dir --upgrade \
+    && /usr/local/bin/python3 -m pip install --no-cache-dir --upgrade \
         pipenv==${PYTHON_PIPENV_VERSION} \
     # Manually create the virtual environment
     && python3 -m venv ${VIRTUAL_ENV} \