[lldb][test] Disable image lookup colour test on Windows

On Linux `main.c` shows up in the symbol search but this is not the
case on Windows according to:
https://lab.llvm.org/buildbot/#/builders/219/builds/7422/steps/6/logs/stdio

It's possible we could make this test work there once function
search highlighting is implemented.

Author: DavidSpickett

lldb/test/Shell/Commands/command-image-lookup-color.test

@@ -1,5 +1,8 @@
 # RUN: %clang_host -g %S/Inputs/main.c -o %t
 
+# The file main.c is does not show up in search on Windows.
+# UNSUPPORTED: system-windows
+
 # Checking simple regex search
 
 # RUN: %lldb %t -b -o 'settings set use-color true' -o 'image lookup -r -s ma' | FileCheck %s --check-prefix CHECK1