cardano-wasm: use envoy-bin in wasm nix devshell

This patch makes the wasm nix devshell use envoy-bin instead of envoy
from nixpkgs, given envoy build on nixos hydra has been broken for a
long time: NixOS/nixpkgs#438433. This is
also blocking ghc-wasm-meta from upgrading to nixos-25.11 nixpkgs
channel at the moment, since cardano-wasm build is included as a part
of our integration tests.

Author: TerrorJack

flake.nix

@@ -252,7 +252,7 @@
                   wasm.secp256k1
                   wasm.blst
                 ]
-                ++ lib.optional (system == "x86_64-linux" || system == "aarch64-linux") wasm-pkgs.envoy;
+                ++ lib.optional (system == "x86_64-linux" || system == "aarch64-linux") wasm-pkgs.envoy-bin;
             };
           };
         playwrightShell = let