Add changelog entry for String#scrub frozen replacement issue

bjfish · eregon · commit c13f13086cca · 2021-07-13T11:59:44.000+02:00
(cherry picked from commit 37fdd83)
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,7 @@ Bug fixes:
 * `rb_funcall()` now releases the C-extension lock (similar to MRI).
 * Fix `rb_str_modify_expand` to preserve existing bytes (#2392).
 * Fix `Marshal.load` of multiple `Symbols` with an explicit encoding (#1624).
+* Fix `String#scrub` when replacement is frozen (#2398, @LillianZ).
 
 Compatibility:
 
