Continues on the work of #1077 by moving the test fixtures into the
`secure_endpoint` fixture and adding a test for it in
`test_secure_api.py`.
The test will check whether an api key in the query will not lead to an
error when `strict_validation` is enabled.
This PR refactors our tests to prepare the activation of our tests for
our AsyncApp.
The separate commits are atomic, which can be useful for reviewing.
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Co-authored-by: Ruwann <ruwanlambrichts@gmail.com>
