bump to latest stable patch release

Hello maintainers,

thank you for importing WPE + related libraries from Debian upstream to the focal repositories, really helps me maintain the wpe-webkit-mir-kiosk snap [1].

The version of libwpebackend-fdo in focal repos is still at 1.6.0-1, while the latest stable release is 1.6.1 [2]. As I understand it, patch updates are alright within a Ubuntu version's packaging policy. Would it be possible to update the package to the latest stable release?

I also filed the same question with:
* libwpewebkit – focal at 2.28.1, upstream at 2.28.4
* cog – focal at 0.4.0-2, upstream at 0.6.0 which is also the version recommended by the WPE team for use with WPE 2.28.x [3]

Thanks in advance,
Tobias

[1] https://snapcraft.io/wpe-webkit-mir-kiosk
[2] https://wpewebkit.org/code/
[3] https://wpewebkit.org/release/schedule/