venv can't figure out that it's isolated

Bug report

Bug description:

I installed python3.13 on my Macbook Pro M1 using Homebrew.

I create venv, activate it and trying to install package. But I'm getting this error:
ERROR: Can not perform a '--user' install. User site-packages are not visible in this virtualenv.

I figured out that I can force pip to think that it's isolated. I just added following line in venv/bin/pip3:

#...
if __name__ == '__main__':
    sys.argv.append("--isolated") # i added this line

It worked.

I don't know exactly where is problem: in pip or in venv. But in latest pip version there is the same error, so maybe it's not pip, idk. Or maybe I did something wrong, or maybe homebrew package is broken, idk.

As I remember, in python3.12 that I also installed using Homebrew there was no such error, everything worked out of box perfectly.

CPython versions tested on:

3.13

Operating systems tested on:

macOS

仮想環境とパッケージのインストールを使って、報告された macOS Homebrew Python 3.13 のセットアップを再現し、その後、生成された venv/bin/pip3 エントリポイントと、--user と --isolated の相互作用を調査します。動作が venv と pip のどちらに属するのかを特定します。担当するコンポーネントが特定され、回帰または期待される動作が適切なテストでカバーされれば完了です。