modules/snipe-it: disable upstream module

NixOS 22.05 will have a module for Snipe-IT, but it's incompatible to
our implementation and the snipe-it package is currently still at 5.x.
So we'll keep our module around and disable the upstream module when
our's is used.  This will give users of our module a chance to migrate
to upstream and upstream a change to update the package to 6.x.

flake.lock

@@ -2,16 +2,16 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1653368995,
-        "narHash": "sha256-v1ztHn+OcA3dAgk6u3pq0d5ol4K/iXwsiFYpNDIN0VE=",
+        "lastModified": 1642961095,
+        "narHash": "sha256-RLatktZmvwFBOyqdoIk4qdS4OGKB7aKIvvs4ZP2L8D8=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "fb0003cd0b4d850995ff439621b01a8a6433cf2d",
+        "rev": "604c44137d97b5111be1ca5c0d97f6e24fbc5c2c",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "release-22.05",
+        "ref": "nixos-21.11-small",
         "repo": "nixpkgs",
         "type": "github"
       }

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "meterriblecrew.net package flake";
 
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/release-22.05";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11-small";
 
   outputs = inputs@{ self, nixpkgs }: let