Age Warning Immersive Headline Gap And Overlap

There are two related issues with the age warning on immersives:

1. On wider breakpoints a gap in the headline background.
2. On narrower breakpoints the background obscures the age warning.

## Screenshots

| | `mobileLandscape` | `mobileLandscape` and above |
|--------|--------|--------|
| No series | ![no-series-mobile-landscape] | ![no-series-desktop] |
| Series | ![series-mobile-landscape] | ![series-desktop] |

[series-desktop]: https://github.com/guardian/dotcom-rendering/assets/53781962/5a92ae58-3410-40a9-af82-fedc68ae9405
[series-mobile-landscape]: https://github.com/guardian/dotcom-rendering/assets/53781962/6a33f5e2-f1c4-4e9c-bc1b-4b4a17686588
[no-series-desktop]: https://github.com/guardian/dotcom-rendering/assets/53781962/171932b7-e274-49cb-8497-d0581aa94386
[no-series-mobile-landscape]: https://github.com/guardian/dotcom-rendering/assets/53781962/ab12c7d2-283a-4b7d-9e05-529f7a4a1080

Articles used:

- https://www.theguardian.com/stage/2023/aug/13/actor-patsy-ferran-streetcar-pygmalion-eliza-doolittle
- https://www.theguardian.com/society/2023/aug/29/martin-luther-king-told-me-i-wouldnt-see-50-the-long-momentous-life-of-clarence-b-jones