Use assertSame instead of deepEquals if actual is a mock

Description

Fixes # (2639)

Automated tests: utbot-samples pipeline as a set of regression checks Manual tests: scenario from issue

[x] I've set the proper labels for my PR (at least, for category and component).
[x] PR title and description are clear and intelligible.
[x] I've added enough comments to my code, particularly in hard-to-understand areas.
[x] The functionality I've repaired, changed or added is covered with automated tests.
[ ] Manual tests have been provided optionally.
[x] The documentation for the functionality I've been working on is up-to-date.