Use block parameter rather than $1 during gsub! so ActiveSupport::SafeBuffer values aren't mangled.

Fixes #15064

activesupport/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Fixed an issue when using
+    `ActiveSupport::NumberHelper::NumberToDelimitedConverter` to
+    convert a value that is an `ActiveSupport::SafeBuffer` introduced
+    in 2da9d67.
+
+    For more info see #15064.
+
+    *Mark J. Titorenko*
+
 *   `TimeZone#parse` defaults the day of the month to '1' if any other date
     components are specified. This is more consistent with the behavior of
     `Time#parse`.

activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb

@@ -13,7 +13,9 @@ def convert
 
         def parts
           left, right = number.to_s.split('.')
-          left.gsub!(DELIMITED_REGEX) { "#{$1}#{options[:delimiter]}" }
+          left.gsub!(DELIMITED_REGEX) do |digit_to_delimit|
+            "#{digit_to_delimit}#{options[:delimiter]}"
+          end
           [left, right].compact
         end
     end

activesupport/test/number_helper_test.rb

@@ -97,6 +97,7 @@ def test_to_delimited
           assert_equal("123,456,789.78901", number_helper.number_to_delimited(123456789.78901))
           assert_equal("0.78901", number_helper.number_to_delimited(0.78901))
           assert_equal("123,456.78", number_helper.number_to_delimited("123456.78"))
+          assert_equal("123,456.78", number_helper.number_to_delimited(ActiveSupport::SafeBuffer.new("123456.78")))
         end
       end