Combine plan maintenance into a single paragraph

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: aclark4life

.github/INCIDENT_RESPONSE.md

@@ -320,10 +320,7 @@ When a CVE is published for a bundled C library:
 
 ## 11. Plan Maintenance
 
-This document is a living record. It should be kept current so it is useful when an
-incident actually occurs.
-
-- **Quarterly review** — revisit during the [Section 1.3 readiness review](#13-readiness-review) at each quarterly release.
+This document is a living record. It should be kept current so it is useful when an incident actually occurs. Revisit it during the [Section 1.3 readiness review](#13-readiness-review) at each quarterly release.
 
 ---