Open the About popup the first time a new version starts

The last version the About popup was shown for is saved as last_seen_version in
settings.cfg. When the game starts with another version, About opens to show
what is new.

tests/fakes/ui_tour.gd

@@ -170,6 +170,7 @@ static func prepare_autoloads() -> void:
 	Settings.hide_next_track = true
 	Settings.use_low_played_mode = false
 	Settings.winning_score = 20
+	Settings.last_seen_version = Settings.version
 	# The inspiration list scrolls by itself, which would make every picture different
 	Settings.inspiration_list_speed = 0