Bump ACTS to v31.2.0

Release notes

• https://github.com/acts-project/acts/releases/tag/v31.2.0
• https://github.com/acts-project/acts/releases/tag/v31.1.0

Compilation changes

• Renaming in the Acts::Experimental namespace, which is by-definition considered non-public API.

Output changes

• ✅ No output changes from ACTS expected