Copy from bpo-39505

When windows users use "python -m venv ENV_DIR", a python virtual environment will be created in ENV_DIR.
Powershell users use ENV_DIR\Scripts\Activate.ps1 to activate virtual environment.
In powershell, a environment variable, "$env:VIRTUAL_ENV", is set and used by many tools to determine that there is an activated venv. In bash, it is "$VIRTUAL_ENV"
In python3.8 and python3.9, $env:VIRTUAL_ENV has a redundant '/', for example:

PS C:\Users\Test> python -m venv test_venv
PS C:\Users\Test> .\test_venv\Scripts\Activate.ps1
PS C:\Users\Test> $env:VIRTUAL_ENV
C:\Users\Test\test_venv/

using python3.7, or using virtualenv with python3.8 or 3.9, or in linux, there will be no such a '/' in the end.

This '/' matters because many tools use this environment variable, for example, oh-my-posh will take "test_venv/" as virtual environment name rather than "test_venv"(Although venv's activate.ps1 itself's default prompt is correct). And from the perspective of semantics and consistency with other platform, the '/' is redundant.

https://bugs.python.org/issue39505