Resolves https://github.com/actions/create-github-app-token/issues/106
- Fixes the parsing to cope with whitespace in the input string.
- Allows the input to be comma or newline-separated. (I've done this for
all array-type inputs in my own actions, but I'm happy to remove this if
you only want to support comma-separated.)
- Added tests for parsing comma and newline-separated inputs.
