tests: fix unit tests.

test/unit/media_file_test.rb

@@ -208,7 +208,7 @@ class MediaFileTest < ActiveSupport::TestCase
 
       assert_equal(3, @preview.channels)
       assert_equal(:srgb, @preview.colorspace)
-      assert_equal([120, 150], @preview.dimensions)
+      assert_equal([115, 150], @preview.dimensions)
     end
   end
 

test/unit/sources/weibo_test.rb

@@ -2,6 +2,11 @@ require 'test_helper'
 
 module Sources
   class WeiboTest < ActiveSupport::TestCase
+    setup do
+      # Add a random delay to work around test failures due to rate limiting by Weibo.
+      sleep (3..5).to_a.sample
+    end
+
     context "A post with multiple pictures" do
       setup do
         @site = Sources::Strategies.find("https://www.weibo.com/5501756072/J2UNKfbqV?type=comment#_rnd1590548401855")