AMDGPU: Mark test as XFAIL in expensive_checks builds

One of the tests added in 93220e7
fails the machine verifier after allocation, but this is a separate
issue.

Author: arsenm

llvm/test/CodeGen/AMDGPU/swdev502267-use-after-free-last-chance-recoloring-alloc-succeeds.mir

@@ -1,5 +1,8 @@
+# XFAIL: expensive_checks
+# FIXME: This fails the machine verifier after allocation
+
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
-# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx942 -stress-regalloc=4 -start-before=greedy,2 -stop-after=virtregrewriter,2  -o - %s | FileCheck %s
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx942 -stress-regalloc=4 -start-before=greedy,2 -stop-after=virtregrewriter,2 -o - %s | FileCheck %s
 
 # This testcase hit a situation where greedy would hit a use after
 # free during last chance recoloring. This case successfully allocates