fix: Build the ChromeNotFoundError message as one string

[Blizzeq]

Description

Chromium passed the "browser not found" message to ChromeNotFoundError as two arguments, because of a stray comma between the f-strings. So str(e) printed a tuple:

('Browser not found. ... Local copy ignored: False. ', 'Path calculated:: /nonexistent/chrome.')

The message is now one string, and the doubled colon after "Path calculated" is gone. A test in test_chromium.py checks both. It fails on main.