Fix the mutation test setup

[Stephan202]

See #972 (comment) and pitest/pitest-junit5-plugin#105. This largely reverts #973.

I'll rebase #972 on top of this PR to prove that this fixes things, but one can also run ./run-mutation-tests.sh locally to do the same.

Suggested commit message:

Fix the mutation test setup (#976)

This largely reverts commit dff67fecbceccde17c4839e37c73dc66a9c65c0f,
avoiding the issue described in pitest/pitest-junit5-plugin#105.

[github-actions]

Looks good. No mutations were possible for these changes.
Mutation testing report by Pitest. Review any surviving mutants by inspecting the line comments under Files changed.

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[mohamedsamehsalah]

Nice that we detected this early.