gs-app-row: Use a lighter red for a warning text in the dark theme

This uses the same color as the Adwaita-dark theme for the @error_color,
which has a better contrast in the dark theme.

Closes #1724
3 jobs for 1724-requires-additional-permissions-text-has-low-contrast-when-using-dark-mode in 2 minutes and 32 seconds (queued for 1 second)