[lldb][test] Disable image lookup colour test on Mac OS

I think it can work there but we need to correct the CHECK lines.

```
command-image-lookup-color.test:34:11: error: CHECK7: expected string not found in input
          ^
```
https://green.lab.llvm.org/green/view/LLDB/job/as-lldb-cmake/10880/testReport/

I don't have a way to see the full output.