Update file placement and discovery about hidden files/folders behavior

[fflaten]

I am following the convention recommended here: https://pester.dev/docs/usage/file-placement-and-naming to place my tests " in a separate tests directory that follows the same directory structure as the main src directory."

Since the code being tested is in .github, the tests are in tests/.github

I'll update the page with a note about dot-prefixed files and folders being hidden on Unix. Will also have to update docs about the behavior of hidden files/folders.

Originally posted by @fflaten in https://github.com/pester/Pester/issues/2515#issuecomment-2199580429

[fflaten]

Currently following PowerShell defaults where hidden items are excluded. E.g. Explicit path to hidden folder will include files in the hidden folder, unless the files are also hidden, then they have to be mentioned explicitly.