ci: update flake.lock

Flake lock file updates:

• Updated input 'flake-utils':
    'github:numtide/flake-utils/d465f4819400de7c8d874d50b982301f28a84605' (2024-02-28)
  → 'github:numtide/flake-utils/b1d9ab70662946ef0850d488da1c9019f3a9752a' (2024-03-11)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/9099616b93301d5cf84274b184a3a5ec69e94e08' (2024-02-28)
  → 'github:NixOS/nixpkgs/d8fe5e6c92d0d190646fb9f1056741a229980089' (2024-03-29)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/72fa0217f76020ad3aeb2dd9dd72490905b23b6f' (2024-02-29)
  → 'github:oxalica/rust-overlay/f258266af947599e8069df1c2e933189270f143a' (2024-03-31)

Author: github-actions[bot]

flake.lock

@@ -64,7 +64,7 @@
           nodejs = fixedNode;
         };
 
-        rustChan = pkgs.rust-bin.stable."1.75.0".default.override {
+        rustChan = pkgs.rust-bin.stable."1.77.1".default.override {
           targets = [];
           extensions = [
             "clippy"