Ignore SECURITY.md in R builds (#220)

Co-authored-by: Zac Davies <zachary.davies+data@databricks.com>

Author: zacdav-db

.Rbuildignore

@@ -9,6 +9,7 @@
 ^\.covrignore$
 ^LICENSE\.md$
 ^NOTICE
+^SECURITY\.md$
 ^cran-comments\.md$
 ^CLAUDE.md
 ^\.claude