Fix Unit tests to be compatible with PHP8.1

[karyna-t]

Fix Unit tests to be compatible with the upcoming PHP 8.1 release.
Need to run all unit tests on PHP8.1 environment and fix all issues (e.g. problems with Deprecation)

Expected result (*)

Unit Tests build is green on PHP 7.4, 8.0, and 8.1 environments
Magento related issues fixed on PHP 8.1

Actual result (*)

Errors and failures on PHP 8.1. env

[m2-assistant]

Hi @karyna-tsymbal-atwix. Thank you for your report.
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[anzin]

@magento I am working on this