Fix type-checking bug from PR #30615. That PR checked if a value was a unicode string using isinstance(debug_info_str, str). But in Python 2.x, str is the byte-string type. So check against bytes instead.

PiperOrigin-RevId: 259873125

tensorflow/lite/python/BUILD

@@ -111,7 +111,6 @@ py_test(
     srcs = ["lite_v2_test.py"],
     srcs_version = "PY2AND3",
     tags = [
-        "no_oss",
         "no_windows",
     ],
     deps = [

tensorflow/lite/python/convert.py

@@ -161,7 +161,7 @@ def toco_convert_protos(model_flags_str,
       # Some of the subtests within the "convert_test" unit-test fail
       # with the error shown above. So watch out for that scenario and
       # convert debug_info_str to bytes where needed
-      if isinstance(debug_info_str, str):
+      if not isinstance(debug_info_str, bytes):
         fp_debug.write(debug_info_str.encode("utf-8"))
       else:
         fp_debug.write(debug_info_str)