Issue 274: test if CI accesses secrets on repo forks

[willi-mueller]

Tell us what you do here

• implementing verified source (please link a relevant issue labelled as verified source)
• fixing a bug (please link a relevant bug report)
• improving, documenting, customizing existing source (please link an issue or describe below)
• anything else (please link an issue or describe below)

Relevant issue

Reproducing a suspected defect where:

1. secrets provided in DLT_SECRETS_TOML are not picked up by the CI test runs on forks
2. changing a single source causes multiple sources to be tested. Adding a new source, however, only causes a run of the new source

I received the shopify secret and added it to github actions.

This reproduces the issue #247

More PR info

Slack conversation with @rudolfix is already running.

[rudolfix]

OK we've got it working on the other PR