Build With Open3D-ML Looks for `main` branch, should be Open3D version tag for reproducible builds

[essandess]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Steps to reproduce the issue

I’ve submitted a MacPorts Portfile for Open3D at macports/macports-ports#32787

When building with BUNDLE_OPEN3D_ML=ON I attempted to checkout Open3D-ML with the same version tag as Open3D to achieve a reproducible build. But the build system throws an error if branch main isn’t checked out.

I believe that Open3D with BUNDLE_OPEN3D_ML=ON should build with the same, fixed version of Open3D-ML.

See, e.g.,

Open3D/util/ci_utils.sh

Line 155 in 0333798

# the build system of the main repo expects a main branch. make sure main exists

Error message

Branch `main` not checked out.

Open3D, Python and System information

NA

Additional information

No response