Auto merge of #29356 - mukilan:mukilan/fix-gstreamer-version-on-mac, r=delan

Update gst plugin for videoconvert & videoscale elements

GStreamer 1.22 has [merged](d11f13f476 (0f8c6b125485c13b682ebcb8fd2f7266439ac317)) the 'gstvideoscale' and 'gstvideoconvert' plugins into a new 'gstvideoconvertscale' plugin.  Since we hardcode the plugin names [here](https://github.com/servo/servo/blob/master/python/servo/gstreamer.py#L68) and [here](https://github.com/servo/servo/blob/master/python/servo/gstreamer.py#L71), to support packaging them with the binary, the builds on MacOS have started to fail since Homebrew upgraded to 1.22.

This PR is a temporary fix to allow CI builds to succeed & PRs to be merged.

 I see code path in the packaging logic for Windows msvc also relies on these plugin names when media-stack is set to 'gstreamer' (I believe it is 'dummy' by default and on nightlies). Ideally, we should fix the packaging logic so that it can handle both older versions of GST (<1.22) and both mac & win platforms. I'll follow up on this with an new issue.

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- [X] These changes fix #29344

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python/servo/gstreamer.py

@@ -65,10 +65,9 @@ GSTREAMER_PLUGINS = [
     ("gstrtpmanager", "gst-plugins-good"),
     ("gsttheora", "gst-plugins-base"),
     ("gsttypefindfunctions", "gst-plugins-base"),
-    ("gstvideoconvert", "gst-plugins-base"),
+    ("gstvideoconvertscale", "gst-plugins-base"),
     ("gstvideofilter", "gst-plugins-good"),
     ("gstvideoparsersbad", "gst-plugins-bad"),
-    ("gstvideoscale", "gst-plugins-base"),
     ("gstvorbis", "gst-plugins-base"),
     ("gstvolume", "gst-plugins-base"),
     ("gstvpx", "gst-plugins-good"),