Enable WPC test in CI

[rosell-dk]

WPC was tested in travis, but it is not tested since we moved to github actions.

We must set the following environment variables to enable test WEBPCONVERT_WPC_API_URL_API0 WEBPCONVERT_WPC_API_URL

env can be set with "env": https://docs.github.com/en/actions/learn-github-actions/environment-variables

I however do not wish to expose the URLs to the world. In travis, you could set ENV in backend, perhaps we can do that in github actions too? Yes we can: https://docs.github.com/en/actions/security-guides/encrypted-secrets

[rosell-dk]

Needs to add them in the workflow, like this:

    env:
      WEBPCONVERT_EWWW_API_KEY: ${{ secrets.WEBPCONVERT_EWWW_API_KEY }}
      WEBPCONVERT_WPC_API_URL: ${{ secrets.WEBPCONVERT_WPC_API_URL }}
      WEBPCONVERT_WPC_API_KEY: ${{ secrets.WEBPCONVERT_WPC_API_KEY }}
      WEBPCONVERT_WPC_API_URL_API0: ${{ secrets.WEBPCONVERT_WPC_API_URL_API0 }}

https://www.edwardthomson.com/blog/github_actions_11_secrets.html