[23857] Branch out 4.3.0

[MiguelCompany]

Description

This makes the master branch be 4.3.x, in preparation for the next minor release 4.3.0

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A: Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A: Any new/modified methods have been properly documented.
• NO: Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• N/A: Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.