refactor(flake.lock): remove obsolete nixpkgs_5 entry and update nixvim inputs

flake.lock

@@ -389,26 +389,12 @@
         "type": "github"
       }
     },
-    "nixpkgs_5": {
-      "locked": {
-        "lastModified": 1787631388,
-        "narHash": "sha256-vMiXptXarfSdJb1Gkc+FYVOAibuBRj7qxGa8z68q1Uw=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "ac6b2166e7a9375683b8e98f860f273222337b16",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "nixvim": {
       "inputs": {
         "flake-parts": "flake-parts_2",
-        "nixpkgs": "nixpkgs_5",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
         "systems": "systems_3"
       },
       "locked": {