mimecast: add 1.0.1 CHANGELOG entry (#23730)

* mimecast: add 1.0.1 CHANGELOG entry

Document error-handling improvements shipped with crawler-sdk 23.4.1
(elevated 500 logging, 429 RateLimitError routing).

* Apply suggestion from @joepeeples

Co-authored-by: Joe Peeples <joe.peeples@datadoghq.com>

---------

Co-authored-by: Joe Peeples <joe.peeples@datadoghq.com>

Author: apiazza-dd

mimecast/CHANGELOG.md

@@ -1,5 +1,11 @@
 # CHANGELOG - mimecast
 
+## 1.0.1 / 2026-05-18
+
+***Fixed***:
+
+* Improve error handling for elevated 500 errors and surface clearer 429 rate-limit errors
+
 ## 1.0.0 / 2024-06-17
 
 ***Added***: