nixos/cloudflared: fix cert.pem installation (#407128)

Changed files
+1 -1
nixos
modules
services
networking
+1 -1
nixos/modules/services/networking/cloudflared.nix
···
RuntimeDirectoryMode = "0400";
LoadCredential = [
"credentials.json:${tunnel.credentialsFile}"
-
] ++ (lib.optional (certFile != null) "cert.pem:certFile");
+
] ++ (lib.optional (certFile != null) "cert.pem:${certFile}");
ExecStart = "${cfg.package}/bin/cloudflared tunnel --config=${mkConfigFile} --no-autoupdate run";
Restart = "on-failure";