vlc-debian-unstable: bump for gcovr 7.0

Gcovr 7.0[^1] fixes issue gcovr/gcovr#841[^2] which was preventing from
merging data from multiple sources correctly.

[^1]: https://github.com/gcovr/gcovr/releases/tag/7.0
[^2]: https://github.com/gcovr/gcovr/pull/844