UploadedMedia: Add missing disposition_type to Content-Disposition

Set it to `inline` because the vast majority of what's sent is multimedia
content while `attachment` would have the side-effect of triggering a
download dialog.

Closes: https://git.pleroma.social/pleroma/pleroma/-/issues/3114

changelog.d/3873.fix

@@ -0,0 +1 @@
+UploadedMedia: Add missing disposition_type to Content-Disposition

lib/pleroma/web/plugs/uploaded_media.ex

@@ -37,7 +37,7 @@ defmodule Pleroma.Web.Plugs.UploadedMedia do
         %{query_params: %{"name" => name}} = conn ->
           name = String.replace(name, "\"", "\\\"")
 
-          put_resp_header(conn, "content-disposition", "filename=\"#{name}\"")
+          put_resp_header(conn, "content-disposition", "inline; filename=\"#{name}\"")
 
         conn ->
           conn

test/pleroma/web/plugs/uploaded_media_plug_test.exs

@@ -37,7 +37,7 @@ defmodule Pleroma.Web.Plugs.UploadedMediaPlugTest do
 
     assert Enum.any?(
              conn.resp_headers,
-             &(&1 == {"content-disposition", "filename=\"\\\"cofe\\\".gif\""})
+             &(&1 == {"content-disposition", "inline; filename=\"\\\"cofe\\\".gif\""})
            )
   end
 end