d/control: Replace libgdk-pixbuf2.0-dev with libgdk-pixbuf-2.0-dev
Since Debian 11, libgdk-pixbuf2.0-dev is a deprecated transitional package that pulls in headers for both gdk-pixbuf (maintained) and gdk-pixbuf-xlib (obsolete). Weston only needs gdk-pixbuf.
Closes: #1037407
I have confirmed (using diffoscope) that this change does not have any effect on the built binary packages.