ciflow/xpu/185468: Fix test_bad_cast to expect BackendCompilerFailed on XPU

XPU uses the same Triton codegen path as CUDA, which asserts on direct

fp8-to-fp8 type conversions (float8_e4m3fn <-> float8_e5m2) in

_get_min_elements_per_thread. However, test_bad_cast only expected

this error for CUDA devices. XPU fell into the else (CPU) branch,

which expects the conversion to succeed, causing the test to fail.

Fix by adding "xpu" to the device condition so XPU correctly expects

BackendCompilerFailed, and remove the @skipIfXpu decorator since the

test now passes on XPU.

Fixes intel/torch-xpu-ops#2888

Test Plan:

python test/inductor/test_fp8.py TestFP8TypesXPU.test_bad_cast_xpu

Authored by Claude.