Update 7.3.0 security note (#478)

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## Summary by CodeRabbit

* **Documentation**
* Updated release notes for version 7.3.0 to clarify kernel security
patches, including corrected CVE references and explicit descriptions of
addressed local privilege escalation vulnerabilities.

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Co-authored-by: “ljm42” <“larry_meaney@iname.com”>

Author: ljm42

docs/unraid-os/release-notes/7.3.0.md

@@ -41,7 +41,7 @@ If you are considering any rollback path below `7.3.0`, also see the [7.2.6 rele
 
 - Security: Add WebGUI security hardening for authenticated-session request handling. This fix is already included in 7.2.5.
 - Security: Update packages
-- Security note: The included 7.3 kernel contains the fix for CVE-2026-31431, the Copy Fail local privilege escalation vulnerability as well as CVE-2025-43284 Dirty Frag local privilege escalation vulnerability.
+- Security note: The included 7.3 kernel patches two local privilege escalation vulnerabilities: Copy Fail (CVE-2026-31431) and Dirty Frag (CVE-2026-43284 and CVE-2026-43500)
 
 ### Onboarding and internal boot