forward options when calling #promote_cached to promote_block (#689)

If `Shrine::Attacher.promote_block { |**options| ... }` is declared with
backgrounding plugin and we call `attacher.promote_cached(**options)`,
the options were not being forwarded to the `.promote_block`.

lib/shrine/plugins/backgrounding.rb

@@ -69,7 +69,7 @@ def destroy_block(&block)
  # Does a background promote if promote block was registered.
  def promote_cached(**options)
  if promote? && promote_block
- promote_background
+ promote_background(**options)
  else
  super
  end

test/plugin/backgrounding_test.rb

@@ -124,6 +124,22 @@
  assert @attacher.stored?
  end
 
+ it "forwards additional options to the block" do
+ @attacher.promote_block do |attacher, **options|
+ @job = Fiber.new { attacher.promote(**options) }
+ end
+
+ @attacher.attach_cached(fakeio)
+ @attacher.promote_cached(location: "foo")
+
+ assert @attacher.cached?
+
+ @job.resume
+
+ assert @attacher.stored?
+ assert_equal "foo", @attacher.file.id
+ end
+
  it "calls default promotion when no promote blocks are registered" do
  @attacher.attach_cached(fakeio)
  @attacher.promote_cached