install_python_venv() may upgrade system Python instead of venv

[coderabbitai]

Context

In base-images/utils/aipcc.sh, the install_python_venv() function creates a virtual environment but then uses ${PYTHON} to upgrade pip/setuptools/wheel:

function install_python_venv() {
    # install venv with bundled pip (no --upgrade-deps)
    "${PYTHON}" -m venv "${VIRTUAL_ENV}"

    "${PYTHON}" -m pip install --force-reinstall --upgrade \
            --index-url https://pypi.org/simple/ \
            pip setuptools wheel
}

Issue

Using ${PYTHON} for the pip upgrade may upgrade the system/base Python interpreter instead of the venv's Python, unless PYTHON already points to the venv interpreter.

Note

Per @jiridanek: "the current implementation is what aipcc does" - this follows the existing AIPCC pattern.

Backlinks

• PR: RHAIENG-2042: chore(base-images): use AIPCC-style scripting instead of scl base to add s390x architecture to odh-base-image-cpu-py312-c9s #2690
• Comment: RHAIENG-2042: chore(base-images): use AIPCC-style scripting instead of scl base to add s390x architecture to odh-base-image-cpu-py312-c9s #2690 (comment)
• Requested by: @jiridanek