add monitor scanned at to bsky monitor

spec/lib/tasks/bluesky/monitor_spec.rb

@@ -103,6 +103,9 @@ RSpec.describe Tasks::Bluesky::Monitor do
           expect(post.text).to eq("Check out this image!")
           expect(post.rkey).to eq("test123")
           expect(post.posted_at).to eq(base_time)
+          expect(post.monitor_scanned_at).to be_within(10.seconds).of(
+            Time.current,
+          )
 
           files = post.files.order(:file_order)
           expect(files.count).to eq(2)