gst/src: Avoid unnecessary renegotiations during streaming
Some clients like many camera apps, including Cheese or Snapshot, trigger a lot of unnessecary renegotiations. While arguably that should be solved on a Gstreamer level, we can help out by checking if the preferred new caps are the same that are already in use and skip the renegotiation in this case.
This allows several apps to e.g. take pictures without a slow and heavy stream restart.
Related: https://gitlab.gnome.org/GNOME/snapshot/-/issues/141