Update test_and_deploy.yaml

[silvbarb]

Set threshold for failing check if code coverage decreases upon new commits (see commit f222dd3)

[codecov[bot]]

Welcome to Codecov :tada:

Once merged to your default branch, Codecov will compare your coverage reports and display the results in this comment.

Thanks for integrating Codecov - We've got you covered :open_umbrella:

[mbstadler]

As discussed, let's rather add a unit test instead of increasing test coverage reduction tolerance