DJV open action extensions as set (#5005)

* Allow to open with djv by extension instead of representation name

* Turn extensions into `set` like on base loader class

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Co-authored-by: Jakub Trllo <43494761+iLLiCiTiT@users.noreply.github.com>

openpype/plugins/load/open_djv.py

@@ -20,12 +20,12 @@ class OpenInDJV(load.LoaderPlugin):
     djv_list = existing_djv_path()
     families = ["*"] if djv_list else []
     representations = ["*"]
-    extensions = [
+    extensions = {
         "cin", "dpx", "avi", "dv", "gif", "flv", "mkv", "mov", "mpg", "mpeg",
         "mp4", "m4v", "mxf", "iff", "z", "ifl", "jpeg", "jpg", "jfif", "lut",
         "1dl", "exr", "pic", "png", "ppm", "pnm", "pgm", "pbm", "rla", "rpf",
         "sgi", "rgba", "rgb", "bw", "tga", "tiff", "tif", "img", "h264",
-    ]
+    }
 
     label = "Open in DJV"
     order = -10