[Relax] Fix inline source module cause path too long error (#17354)

When the source is provided as inline string literal, creating `Path`
object causes path too long error.

python/tvm/relax/frontend/nn/extern.py

@@ -228,7 +228,10 @@ def _detect_source_code(source_code) -> str:
                     path = Path(source_code)
                 except:  # pylint: disable=bare-except
                     return source_code
-                if not path.is_file():
+                try:
+                    if not path.is_file():
+                        return source_code
+                except:  # pylint: disable=bare-except
                     return source_code
             with path.open("r", encoding="utf-8") as file:
                 return file.read()