The documentation says the following on passing environment variables:

env: host=api.dev.local,port=4222

When passing the environment variables this way, unfortunately due to GitHub Actions syntax, the variables should be listed in a single line, which can be hard to read.

What a lot of other actions tend to do is allow passing multiple items on multiple lines, making use of YAML's linebreak preserving syntax:

env: |
 host=API.dev.local
 port=4222

In the action code, you can then just do something akin to env.includes("\n") ? env.split("\n") : env.split(",") for improved ergonomics with very little effort.