Fix grammar in Security Copilot prompts section

Corrected grammar in the description of suggested prompts.

Author: guywi-ms

defender-xdr/security-copilot-m365d-incident-summary.md

@@ -61,7 +61,7 @@ Incidents containing up to 100 alerts can be summarized into one incident summar
 - Suggested prompts, which provide insights into the specific assets involved in the incident.
 - Indicators of compromise (IoCs).
 - Names of [threat actors](/unified-secops-platform/microsoft-threat-actor-naming) involved.
-- Suggested Security Copilot prompts, which guide you to focus on the most relevant next steps, gain deeper insight, and simplify investigations.
+- Suggested Security Copilot prompts, which guide you to focus on the most relevant next steps, gain deeper insights, and simplify investigations.
 
 To summarize an incident: