Add a language version tag in spawnHybridUri (dart-lang/web_socket_channel#131)

Code snippets passed to `spawnHybridCode` are currently always run with
the SDK language version. Add an explicit language version marker so
that this test is stable.

Bump min SDK and `package:test` version to one which supports these
markers.
3 files changed
tree: fd0e74519b5fcf39a729697cd5497c43900fbee6
  1. pkgs/