net-mgmt/icinga2: Update to 2.13.5

Changelog:

• Ensure not to write an incomplete (i.e. corrupt) state file. #9467
• ITL: Render vars.apt_upgrade=true as --upgrade, not --upgrade=true. #9458
• Icinga DB: Add missing Redis SELinux policy. #9473
• Windows: Don't spam the event log with non-error startup messages. #9457
• Windows: Update bundled version of OpenSSL. #9460
• Docs: Update RHEL 8 installation instructions. #9482
• Docs: Add RHEL 9 installation instructions. #9482

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