[sdl2] Fix pkgconfig: missing system lib dbus-1

[JackBoosY]

CMake Error at scripts/cmake/vcpkg_fixup_pkgconfig.cmake:232 (message):
  Library "dbus-1" was not found! If it is a system library use the
  SYSTEM_LIBRARIES parameter for the vcpkg_fixup_pkgconfig call! Otherwise,
  correct the *.pc file
Call Stack (most recent call first):
  scripts/cmake/vcpkg_fixup_pkgconfig.cmake:298 (vcpkg_fixup_pkgconfig_check_files)
  ports/sdl2/portfile.cmake:97 (vcpkg_fixup_pkgconfig)
  scripts/ports.cmake:79 (include)

Fixes #13236.

[ras0219-msft]

LGTM, thanks!