[lldb][test] TestFunctionTemplateParameterPack.py: XFAIL instead of skip

This test doesn't trigger an assertion on top-of-tree. Turn this into an
XFAIL instead.

Found this test because I'm working on improving parameter pack support
in the expression evaluator.

GitOrigin-RevId: 42764ec59bc41979663a291fec1c5afdcf0b3fe8
1 file changed