[lldb][test] Disable image dump ast test on Windows

Again I think this requires DWARF. In theory we could use the PDB
file but I suspect that PDB file is in fact empty, because we
tell clang to produce DWARF.

So on Windows, first thing is we cannot run the expressions:
(lldb) expr A(); A1(); BA1(); AB();
error: <user expression 1>:1:1: 'A' has unknown return type; cast the call to its declared return type
    1 | A(); A1(); BA1(); AB();
      | ^~~
...and so on...

And then the AST is all unknown functions:
(lldb) image dump ast
Dumping clang ast for 4 modules.
TranslationUnitDecl 0x2b3bb591870 <<invalid sloc>> <invalid sloc> <undeserialized declarations>
|-FunctionDecl 0x2b3bb592970 <<invalid sloc>> <invalid sloc> mainCRTStartup 'unsigned long (void *)'
| `-ParmVarDecl 0x2b3bb592a20 <<invalid sloc>> <invalid sloc> 'void *'
`-FunctionDecl 0x2b3bb592ad8 <<invalid sloc>> <invalid sloc> __scrt_common_main_seh 'int ()' static

So I'm just going to disable this test on Windows, it's pretty
clear why it doesn't work and we have no plans to make it work.