[Misc] Apply SonarCloud rule cpp:S3230

Description

• Rule name: Do not use the constructor's initializer list for data member. Use the in-class initializer instead.
• Rule code: cpp:S3230
• Rule link: https://sonarcloud.io/project/issues?open=AYjy0_uAx-2o8nUjJbcD&id=cern-cta_CTA

Checklist

• Documentation reflects the changes made.
• Merge Request title is clear, concise, and suitable as a changelog entry. See our contributing docs

References

Closes #1403 (closed)