decodebin2: Do not fail if one of the decoders isn't able to output the requested...

decodebin2: Do not fail if one of the decoders isn't able to output the requested format

when expose-all=False

When trying to find an decoder in that case, we loop over the different
decoder factories, and check that it outputs a format that matches the
requested one (through the :caps property), but if we find a decoder
that do match but later on some other don't we end up failing
autopluging. This patch ensures that we still plug the decoder that can
work.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3011>