Fix unified build of LibWebRTCProviderGStreamer

https://bugs.webkit.org/show_bug.cgi?id=248532

Reviewed by Youenn Fablet.

* Source/WebCore/platform/mediastream/libwebrtc/gstreamer/LibWebRTCProviderGStreamer.h: LibWebRTCProvider.h needs to be included

Canonical link: https://commits.webkit.org/257726@main

Author: blino

Source/WebCore/platform/mediastream/libwebrtc/gstreamer/LibWebRTCProviderGStreamer.h

@@ -29,6 +29,7 @@
 
 #include "GStreamerVideoDecoderFactory.h"
 #include "GStreamerVideoEncoderFactory.h"
+#include "LibWebRTCProvider.h"
 
 namespace WebCore {