[lldb][test] Disable TestSBValueUnsignedEnumBitField.py for old DWARF versions

With older DWARF versions we don't encode the enum's underlying
type in DWARF. In those cases LLDB sign-extends the bitfield as
a signed integer. Without the actual enum type being present in
DWARF there's not much we can do.

Differential Revision: https://reviews.llvm.org/D134734

lldb/test/API/python_api/sbvalue_unsigned_enum_bitfield_value/TestSBValueUnsignedEnumBitField.py

@@ -14,5 +14,7 @@ for this not to happen.
 """
 
 import lldbsuite.test.lldbinline as lldbinline
+from lldbsuite.test.decorators import *
 
-lldbinline.MakeInlineTest(__file__, globals())
+lldbinline.MakeInlineTest(__file__, globals(),
+                          [skipIf(dwarf_version=['<', '3'])])