flake.lock: Update

Flake lock file updates:

• Updated input 'pre-commit-hooks/nixpkgs':
    'github:NixOS/nixpkgs/ac718d02867a84b42522a0ece52d841188208f2c' (2023-03-15)
  → follows 'nixpkgs'

flake.lock

@@ -234,22 +234,6 @@
       }
     },
     "nixpkgs_2": {
-      "locked": {
-        "lastModified": 1678898370,
-        "narHash": "sha256-xTICr1j+uat5hk9FyuPOFGxpWHdJRibwZC+ATi0RbtE=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "ac718d02867a84b42522a0ece52d841188208f2c",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixos-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
-    "nixpkgs_3": {
       "locked": {
         "lastModified": 1627814220,
         "narHash": "sha256-P+MDgdZw2CBk9X1ZZaUgHgN+32pTfLFf3XVIBOXirI4=",
@@ -270,7 +254,9 @@
         "flake-compat": "flake-compat",
         "flake-utils": "flake-utils_2",
         "gitignore": "gitignore",
-        "nixpkgs": "nixpkgs_2",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
         "nixpkgs-stable": "nixpkgs-stable"
       },
       "locked": {
@@ -318,7 +304,7 @@
     "rycee-firefox-addons": {
       "inputs": {
         "flake-utils": "flake-utils_3",
-        "nixpkgs": "nixpkgs_3"
+        "nixpkgs": "nixpkgs_2"
       },
       "locked": {
         "dir": "pkgs/firefox-addons",