disable rsc workflow if the license is empty

[colearendt]

Having a hard time determining that "this PR is coming from a fork"

• github.repository is always set to rstudio/pins
• secrets is not available in the if block

[hadley]

@colearendt I'm going to try this approach that @maelle figured out for pkgdown

[maelle]

For the record I'm fairly positive I copied an approach of @jennybc's e.g. in https://github.com/hadley/r-pkgs/blob/master/.github/workflows/build-book.yaml :grin:

[github-actions[bot]]

This pull request has been automatically locked. If you believe you have found a related problem, please file a new issue (with a reprex: https://reprex.tidyverse.org) and link to this issue.