Specify version for denoland/setup-deno

[haphut]

denoland/setup-deno@v1 was published recently and is used in the
README.md of the action:
https://github.com/denoland/setup-deno/blob/4a4e59637fa62bd6c086a216c7e4c5b457ea9e79/README.md

We should use it, too.

[irealva]

Note for team: we would have to update Deno versions in Flat Editor and demos if we merge this PR. And documentation.

[haphut]

Thanks for the response! I meant to make just a small improvement but I guess it's not that simple.

Currently the only difference between @main and @v1 seems to be the deno download URL. Do you mean that the team needs to update the setup-deno versions in Flat Editor and demos for consistency? EDIT: I assume you do: https://github.com/search?p=1&q=org%3Agithubocto+setup-deno&type=Code . That is a bit of work to fork all of those for a one-line change.