vaultwarden, matrix-sliding-sync: Pin to unstable

These packages are important to keep up-to-date as clients often rely on them
being fully up-to-date.

Change-Id: I934fc7472953094b653aa1349ad28628112f1b7f
Reviewed-on: https://git.clicks.codes/c/Infra/NixFiles/+/628
Reviewed-by: Samuel Shuert <coded@clicks.codes>
Tested-by: Skyler Grey <minion@clicks.codes>
diff --git a/flake.lock b/flake.lock
index 40c87c6..4572654 100644
--- a/flake.lock
+++ b/flake.lock
@@ -453,6 +453,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-unstable": {
+      "locked": {
+        "lastModified": 1712439257,
+        "narHash": "sha256-aSpiNepFOMk9932HOax0XwNxbA38GOUVOiXfUVPOrck=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "ff0dbd94265ac470dda06a657d5fe49de93b4599",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nixpkgs_2": {
       "locked": {
         "lastModified": 1697688401,
@@ -557,6 +573,7 @@
         "nixpkgs-clicksforms": "nixpkgs-clicksforms",
         "nixpkgs-mongodb": "nixpkgs-mongodb",
         "nixpkgs-privatebin": "nixpkgs-privatebin",
+        "nixpkgs-unstable": "nixpkgs-unstable",
         "scalpel": "scalpel",
         "sops-nix": "sops-nix"
       }