Fix NanoVDB CI

[apradhana]

This is an attempt to fix NanoVDB CI. For Windows, this boils down to downgrading the CMake to cmake 3.28. I follow an example given on this page to downgrade the CMake version. Perhaps I should also update the documentation here: https://www.openvdb.org/documentation/doxygen/dependencies.html#depKnownIssues.

I tried the fix that @Idclip suggested for MacOS, but the CI is still failing when the homebrew installs the dependencies.