Combine vinegar, sugar, celery seeds, mustard seeds, pickling spices, dry mustard, turmeric, salt, and ginger in a large pot. Place over high heat and bring to a boil. Reduce heat; simmer for 15 minutes to extract the flavors of the spices. Return heat to high and add tomatoes and onions, stirring to coat everything evenly. Once the liquid begins to boil, immediately shut off the heat and allow mixture to cool to room temperature.