Redis config: Path "/nix/store" is not writable

[Al2Klimov]

Describe the bug

If I change DB settings in the web UI, but latter can't write to /etc/icingaweb2, it shows me the desired file contents, so I can deploy them myself.

However, if I change Redis settings in the web UI, it just says: Path "/nix/store" is not writable.

Admittedly, I was too lazy to also properly test the command transports.

To Reproduce

1. Make /etc/icingaweb2 read-only for PHP user
2. Change Redis settings in the web UI

Expected behavior

All config forms behave like the DB settings.

Screenshots

Your Environment

• Icinga DB Web version (System - About): 1.2.2
• Icinga Web 2 version (System - About): 2.12.4
• Web browser: Safari
• Icinga 2 version (icinga2 --version): 2.15
• Icinga DB version (icingadb --version): 1.4
• PHP version used (php --version): 8.3
• Server operating system and version: NixOS 25.05

Additional context