fix: exclude VPN-only release notes URL from lychee checks (#2103)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: themr0c

.lycheeignore

@@ -8,3 +8,6 @@ file://.*titles-generated/index\.html$
 
 # External sites that block automated requests
 ^https://fonts\.google\.com/icons
+
+# Release notes site is behind Red Hat VPN, unreachable from GitHub Actions
+^https://red-hat-developers-documentation\.pages\.redhat\.com/red-hat-developer-hub-release-notes