Fix pytest installation

[tamarinvs19]

Description

Fix test framework installation process. See #1570.

Fixes #1570

How to test

Manual tests

See #1570

Self-check list

Check off the item if the statement is true. Hint: [x] is a marked item.

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• PR title and description are clear and intelligible.
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• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.