Clarify error message of #19666

[CyrilleB79]

Link to issue number:

Fix-up of #19666

Discussed in #19666 (comment)

Summary of the issue:

The error message as written in #19666 could let think that a drive letter should be added in the portable path definition even when using %temp% which, though, already contains it.

Description of user facing changes:

Rewrote the error message.

Description of developer facing changes:

N/A

Description of development approach:

N/A

Testing strategy:

Check installer

Known issues with pull request:

None

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.