chore(deps): update flake.lock (#6436)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/8be7bd0' (2026-08-14)
  → 'github:NixOS/nixpkgs/391b592' (2026-08-20)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/b211ead' (2026-08-16)
  → 'github:oxalica/rust-overlay/f60c1b5' (2026-08-23)

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1786719841,
-        "narHash": "sha256-QcpQOT0NQEFkI77t+YXPZqDJc35iIodG7zinieOwFUg=",
+        "lastModified": 1787209939,
+        "narHash": "sha256-WvvHR4kSQLAbtouMC/ruZ5UpLwlUcY3K4FAllMN+yGk=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "8be7bd0c83f12e2e3bbba07c9044d6fed9e66f7f",
+        "rev": "391b592eb44808b3bd0cb80bb71b63a5a118b8bb",
         "type": "github"
       },
       "original": {
@@ -29,11 +29,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1786849542,
-        "narHash": "sha256-MS8cOa/ii1+QA8R3JWVzqEIoXimu9n50GwQDiBVTFOM=",
+        "lastModified": 1787454509,
+        "narHash": "sha256-r4LDUF+zmJnkftvCVkCrUhSJazsf6EVJF+V2l4/MYbI=",
         "owner": "oxalica",
         "repo": "rust-overlay",
-        "rev": "b211eadeba8b180da9453ec3413a8a3535c85b3f",
+        "rev": "f60c1b57ff805a46b5175c76fc981fb4f81efbcc",
         "type": "github"
       },
       "original": {