meson: Add missing pbutils dependency to multifile

meson: Add missing pbutils dependency to multifile

Found via the Jenkins CI:

FAILED: subprojects/gst-plugins-good/gst/multifile/gstmultifile@sha/gstsplitmuxsink.c.o
[...]
In file included from ../subprojects/gst-plugins-good/gst/multifile/gstsplitmuxsink.h:24:0,
                 from ../subprojects/gst-plugins-good/gst/multifile/gstsplitmuxsink.c:59:
../subprojects/gst-plugins-base/gst-libs/gst/pbutils/pbutils.h:30:43: fatal error: gst/pbutils/pbutils-enumtypes.h: No such file or directory
 #include <gst/pbutils/pbutils-enumtypes.h>
                                           ^
compilation terminated.

https://ci.gstreamer.net/job/GStreamer-master-meson/263/console