darwin.libiconv: disable test timeouts (#401183)

pkgs/os-specific/darwin/apple-source-releases/libiconv/package.nix

···
   # Can’t use `mesonCheckPhase` because it runs the wrong hooks for `installCheckPhase`.
   installCheckPhase = ''
     runHook preInstallCheck
-    meson test --no-rebuild
+    meson test --no-rebuild --print-errorlogs --timeout-multiplier=0
     runHook postInstallCheck
   '';