Set `max-width` on injected bounding box

[kljohann]

max-width of the injected element is set to none. Otherwise, the box can be too small if the page's CSS applies to the injected element by accident (e.g., body > * { max-width: 5cm; }).

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📚 Documentation preview 📚: https://shot-scraper--143.org.readthedocs.build/en/143/