Prepare for 9.0.0~pre2 Release

[scpeters]

🎈 Release

Preparation for 9.0.0~pre2 release.

Comparison to 9.0.0-pre1: gz-math9_9.0.0-pre1...gz-math9

Needed by <PR(s)>

Checklist

• Asked team if this is a good time for a release
• There are no changes to be ported from the previous major version
• No PRs targeted at this major version are close to getting in
• Bumped minor for new features, patch for bug fixes
• Updated changelog
• Updated migration guide (as needed)
• Link to PR updating dependency versions in appropriate repository in gazebo-release (as needed):

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[scpeters]

holding for #692

[azeey]

@scpeters We don't need #692 for python binding support, plus, there's a request for a new release in gazebo-release/gz_math_vendor#15, so please go ahead with the pre2 release. Thanks!

[scpeters]

@scpeters We don't need #692 for python binding support, plus, there's a request for a new release in gazebo-release/gz_math_vendor#15, so please go ahead with the pre2 release. Thanks!

ok, I'll just add #695 to the changelog and proceed