Run Subprocesses in Destination dir

[ehlewis]

• I have added an entry to docs/changelog.md

Summary of changes

Addressing #1091
Set venv creation and install_package subprocesses to run inside the destination directory (self.root) in order to resolve a bug where python files in the cwd could break the venv creation.
Also a slight security improvement since by ignoring the python files in the cwd which could potentially override files on the sys.path

Test plan

Manually tested resolution of bug by creating a file in cwd
echo "blah blah" > logging.py
then running the current release of pipx
pipx install frogmouth
we get the expected error

File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/venv/__init__.py", line 7, in <module>
  import logging
  File "/Users/ehlewis/test/logging.py", line 1
    blah blah
         ^^^^
SyntaxError: invalid syntax

'/Library/Frameworks/Python.framework/Versions/3.12/bin/python3.12 -m venv --without-pip
/Users/ehlewis/.local/pipx/venvs/frogmouth' failed

running the same command with the modified create_venv shows a successful install and the installed package functions as expected

python3 src/pipx install frogmouth                                                 
  installed package frogmouth 0.9.2, installed using Python 3.12.0
  These apps are now globally available
    - frogmouth
done! ✨ 🌟 ✨

Repo tests were also passed successfully
https://github.com/ehlewis/pipx/actions/runs/7072389139

[gaborbernat]

Test please.

[gaborbernat]

Seems stalled, we can reopen if you pick it up again.