[CI] Resolve CI compilation failures on MacOSX

[Lunderberg]

The build on main failed link with the following error message. This first occurred in the post-merge build of #17257, but the failure mode (error message below) doesn't appear related to the changes in that commit.

conda.exceptions.CondaValueError: You have chosen a non-default solver backend (libmamba) but it was not recognized.

[Lunderberg]

After investing, it looks like the failures were due to conda attempting to use a dependency solver that wasn't actually installed in the conda environment. This seems to result from some mix of the following:

1. The most recent release of conda-build now defaults to using libmamba for dependency solving.
2. The current conda-build only requires conda >= 23.7.0
3. The libmamba library is not added as a dependency until conda >= 23.10.
4. Some combination of the python3 versions and the cmake versions that are pinned in TVM requires that conda < 23.10.
5. The configuration for conda-incubator/setup-miniconda@v3 applies the default value of conda-solver based on the conda version in the base environment. This is then specified as an explicit config to be used by the conda version in the tvm-build environment.

If we explicitly specify conda-solver: classic, then we avoid using the missing libmamba at all.