let pinning of nixos-unstable commit happen in flake.lock rather than flake.nix

flake.lock

@@ -17,17 +17,18 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1651726670,
-        "narHash": "sha256-dSGdzB49SEvdOJvrQWfQYkAefewXraHIV08Vz6iDXWQ=",
+        "lastModified": 1652172129,
+        "narHash": "sha256-8e2JMrswaKe02P8rYfvIMoc59pNuw6h/GYu8DBE1c+0=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "c777cdf5c564015d5f63b09cc93bef4178b19b01",
+        "rev": "f419dc5763c2b3c5580e396dea065b6d8b58ee27",
         "type": "github"
       },
       "original": {
-        "id": "nixpkgs",
-        "rev": "c777cdf5c564015d5f63b09cc93bef4178b19b01",
-        "type": "indirect"
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
       }
     },
     "npmlock2nix": {

flake.nix

@@ -1,9 +1,8 @@
 {
   description = "An implementation of the Double Ratchet cryptographic ratchet";
 
-  inputs.nixpkgs.url = "nixpkgs/c777cdf5c564015d5f63b09cc93bef4178b19b01";
-  # c777cdf5c564015d5f63b09cc93bef4178b19b01 is current unstable.  We can't use
-  # the current stable release because of
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  # We can't use the current stable release because of
   # https://github.com/emscripten-core/emscripten/issues/14995
   inputs.flake-utils.url = "github:numtide/flake-utils";
   inputs.npmlock2nix = {