`python -m venv <dir>` cause dir appairs more than one times in $PATH

Bug report

Bug description:

pwd # /home/qcg/py
python3 -m venv .
source bin/activate # or relogin the shell

import os

envs = os.environ['PATH'].split(':')
envs.sort()
print('\n'.join(envs))
#...
#/home/qcg/py/bin
#/home/qcg/py/bin
#...

my fix:
In bin/activate,

PATH="$VIRTUAL_ENV/bin:$PATH"
export PATH

===>

case ":${PATH}:" in
    *:"$VIRTUAL_ENV/bin":*)
        ;;
    *)
        export PATH="$VIRTUAL_ENV/bin:$PATH"
        ;;
esac

Tested on Ubuntu 24.04 (in Windows WSL2) with built-in python 3.12.3.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Reproduce the issue with python3 -m venv . and source bin/activate, then inspect the generated bin/activate entry point and its PATH handling. Confirm that activating the environment does not add its bin directory more than once, including after relogging the shell.