Cortex-M Backend: Skip while_loop test

It has been observed to hang randomly.
Likely, the random input causes the quantizatized
while loop to never finish in some cases.

Signed-off-by: Erik Lundell <erik.lundell@arm.com>
Change-Id: Ie738e923d7595040d9e608a46bbe6851958fa3bd

Author: Erik-Lundell

backends/cortex_m/test/misc/test_portable_int8.py

@@ -683,7 +683,13 @@ def _quantize_and_export(
 }
 
 
-@parametrize("op_case", OP_CASES, xfails=xfails, strict=False)
+@parametrize(
+    "op_case",
+    OP_CASES,
+    xfails=xfails,
+    strict=False,
+    skips={"while_loop": "Has been observed to hang randomly."},
+)
 def test_shared_qspec_portable_int8_ops(op_case: OpCase) -> None:
     tester = CortexMTester(op_case.module, op_case.example_inputs)
     tester.test_dialect(ops_before_transforms={}, ops_after_transforms={})