[emadleo13]

Summary

document the filesystem requirement for collecting tests with
'--pyargs' inside PyInstaller-frozen applications.

• explain why tests stored only inside a PYZ archive cannot be
  collected by pytest's filesystem-based collectors.
• show how to include test sources using the PyInstaller 'datas'
  option.
• add a documentation changelog entry.

Background

Related to #14771.
i reproduced the reported behavior on Arch Linux with
pytest 9.1.1 and PyInstaller 6.21.0.
the frozen application failed to collect tests when they existed
only in the embedded archive. Bundling the source files as data
allowed '--pyargs myapp.test' to collect and run them.
this PR documents the workaround confirmed in the issue discussion.
It does not implement collection from frozen archives.

Validation

• Documentation build: 'uvx tox -e docs ' passed.
• Pre-commit checks for changed files passed.
• 'git diff --check' passed.