Fix UnboundLocalError in manual yt-dlp binary selection

Unpacking getOpenFileName() into a variable named _ made _ local to
select_ytdlp_path(), so the i18n _() calls earlier in the function
raised UnboundLocalError before the file dialog could open, breaking
manual binary selection entirely.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ytsage/core/ytsage_yt_dlp.py

@@ -429,7 +429,7 @@ class YtdlpSetupDialog(QDialog):
         """
         )
 
-        file_path, _ = file_dialog.getOpenFileName(
+        file_path, _selected_filter = file_dialog.getOpenFileName(
             self, _("ytdlp_setup.select_executable_title"), "", file_filter
         )