Fix mockery version downgrade

[Zhaars]

Makefile contains installing the latest mockery version which requires go 1.18. Acra should support at least three latest versions. Just downgrade the mockery version to be able to build Acra with a version lower than 1.18.

Checklist

• [ ] Change is covered by automated tests
• [ ] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [ ] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)