Fix code to support older versions of Ruby

We still support super old versions, yes, and it doesn't like `ensure`
without a `begin..end` unfortunately.

I plan to remove this support soon, but for now I don't want to stop
supporting it yet.

test/test_helper.rb

@@ -27,11 +27,14 @@ class ActiveSupport::TestCase
   if ActiveSupport.version < Gem::Version.new("5.0")
     def assert_deprecated(match, deprecator)
       super(match) do
-        behavior = deprecator.behavior
-        deprecator.behavior = ActiveSupport::Deprecation.behavior
-        yield
-      ensure
-        deprecator.behavior = behavior
+        # TODO: remove extra begin..end when dropping support for Ruby <= 2.4
+        begin
+          behavior = deprecator.behavior
+          deprecator.behavior = ActiveSupport::Deprecation.behavior
+          yield
+        ensure
+          deprecator.behavior = behavior
+        end
       end
     end
   end