Bump Acts Tag to v31.0.0

This bumps ACTS from v30.3.2 to v31.0.0

Release notes of in-between versions:

• v31.0.0

Related to: ATLIDTRKCP-512

Adding here info on PRs affecting vertex from @pagessin 's comment:

It's these four PRs, two of which are a pair of PRs where one reverts the other:

https://github.com/acts-project/acts/issues?q=is%3Aclosed+milestone%3Av31.0.0+sort%3Aupdated-desc+label%3A%22Fails+Athena+tests%22

So this:

• https://github.com/acts-project/acts/pull/2655 (Bugfix for a case where a vertex would not be included in the multi-vertex fit)
• https://github.com/acts-project/acts/pull/2551 (which we believe is a difference from literature calculating an unnecessary division by weight)