flake.lock: Update

Flake lock file updates:

• Added input 'nixpkgsUnstable':
    'github:nixos/nixpkgs/8a86b98f0ba1c405358f1b71ff8b5e1d317f5db2' (2023-09-27)

flake.lock

@@ -55,11 +55,28 @@
         "type": "github"
       }
     },
+    "nixpkgsUnstable": {
+      "locked": {
+        "lastModified": 1695830400,
+        "narHash": "sha256-gToZXQVr0G/1WriO83olnqrLSHF2Jb8BPcmCt497ro0=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "8a86b98f0ba1c405358f1b71ff8b5e1d317f5db2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
         "home-manager": "home-manager",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "nixpkgsUnstable": "nixpkgsUnstable"
       }
     },
     "systems": {