Upgrade Go to 1.26.5 to fix CVE (v5.4.37)

[reinkrul]

Summary

• Upgrade Go to 1.26.5
• Add release notes for v5.4.37

Fixes the following vulnerabilities:

Advisory	Package	Description
GO-2026-5856	crypto/tls (stdlib)	De-anonymization of Encrypted Client Hello (ECH) handshakes: PSK identities were disclosed in the unencrypted client hello, allowing passive network observers to de-anonymize sessions

Assisted by AI

[qltysh]

Coverage Impact

This PR will not change total coverage.

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