[arm] Allow non-utf8 in fb

This is a temp workaround to suppress test failures in
https://github.com/pytorch/executorch/actions/runs/12794699471/job/35670399085

Author: digantdesai

backends/arm/test/runner_utils.py

@@ -653,6 +653,7 @@ def dbg_tosa_fb_to_json(tosa_fb: bytes) -> Dict:
         "flatc",
         "--json",
         "--strict-json",
+        "--allow-non-utf8",  # Temporary workaround for TOSA flatbuffer schema
         "-o",
         tmp,
         "--raw-binary",