sdf 14.6.0 prep

[nkoenig]

🎈 Release

Preparation for 14.6.0 release.

Comparison to 14.5.0: https://github.com/gazebosim/sdformat/compare/sdformat14_14.5.0...sdf14

Needed by <PR(s)>

Checklist

• [x] Asked team if this is a good time for a release
• [x] There are no changes to be ported from the previous major version
• [x] No PRs targeted at this major version are close to getting in
• [x] Bumped minor for new features, patch for bug fixes
• [x] 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.

[nkoenig]

@osrf-jenkins run tests please

[nkoenig]

I targeted the wrong branch...and now I don't know how to get the correct ABI checker to run. I'll close and re-open this.