Update Powsybl-core dependency to 6.1.2

[rolnico]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? No

What kind of change does this PR introduce? Dependency update

What is the current behavior? AFS was using powsybl-core 5.3

What is the new behavior (if this is a feature change)? AFS is now using powsybl-core 6.1.2

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [x] No

If yes, please check if the following requirements are fulfilled

• [ ] The Breaking Change or Deprecated label has been added
• [ ] The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

Other information:

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
78.3% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud