nixos/tests/syncthing: disable syncthing-many-devices test

The `syncthing-many-devices` test has been failing since at least
2025-07-06, and there doesn't appear to be any issue reports relating to
it. Disabling is done simply out of convenience, and an issue has been
reported about it.

Tracking issue: https://github.com/NixOS/nixpkgs/issues/447674
First failing hydra build: https://hydra.nixos.org/build/302090970

nixos/tests/all-tests.nix

@@ -1409,7 +1409,9 @@ in
   syncthing-guiPassword = runTest ./syncthing/guiPassword.nix;
   syncthing-guiPasswordFile = runTest ./syncthing/guiPasswordFile.nix;
   syncthing-init = runTest ./syncthing/init.nix;
-  syncthing-many-devices = runTest ./syncthing/many-devices.nix;
+  # FIXME: Test has been failing since 2025-07-06:
+  # https://github.com/NixOS/nixpkgs/issues/447674
+  # syncthing-many-devices = runTest ./syncthing/many-devices.nix;
   syncthing-no-settings = runTest ./syncthing/no-settings.nix;
   syncthing-relay = runTest ./syncthing/relay.nix;
   sysfs = runTest ./sysfs.nix;

pkgs/applications/networking/syncthing/default.nix

@@ -71,7 +71,6 @@ let
             syncthing-guiPassword
             syncthing-guiPasswordFile
             syncthing-init
-            syncthing-many-devices
             syncthing-no-settings
             syncthing-relay
             ;