changes: Add file for ticket 40674

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/ticket40674

+  o Major bugfixes (relay):
+    - Improve security of our DNS cache by randomly clipping the TTL value.
+      TROVE-2021-009. Fixes bug 40674; bugfix on 0.3.5.1-alpha.