[libc++] Modules tests keep failing on the release/18.x branch

[ldionne]

We should disable the since it borks the rest of the CI.

[ldionne]

/cherry-pick 0bbada9

[llvmbot]

Failed to cherry-pick: 0bbada9

https://github.com/llvm/llvm-project/actions/runs/8283300691

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request