iced-template: avoid duplicating Cargo.lock in nix store

(to reduce rebuilds)
crane does something similar automatically

flake.nix

@@ -47,7 +47,7 @@
           src = lib.sourceFilesBySuffices ./. [
             "Cargo.toml"
             "Cargo.lock"
-            "*.rs"
+            ".rs"
           ];
         };