Fix invalid escape sequence (#790)

Summary:
Pull Request resolved: #790

Fixes:
```
/re_cwd/buck-out/v2/gen/fbcode/3c31cd45381cab49/aitemplate/AITemplate/fb/pt-ops/fmha_attention/__test_fmha_attention_op__/test_fmha_attention_op#link-tree/aitemplate/backend/cuda/target_def.py:393: DeprecationWarning: invalid escape sequence '\,'
```

Reviewed By: kadeng

Differential Revision: D46947138

fbshipit-source-id: 81c77e3f094f3b1cb13448be3f37c4492591429a

python/aitemplate/backend/cuda/target_def.py

@@ -390,7 +390,7 @@ def _build_compile_options(self):
                 self.nvcc_options_json["args"]
                 + ["-I" + path for path in include_paths]
                 + [
-                    f"-Xcompiler '-Wp\,@{fb_include_path}'",  # noqa: W605
+                    f"-Xcompiler '-Wp\\,@{fb_include_path}'",
                     "-Xcompiler -Wno-strict-aliasing",
                     "-Xcompiler -Wno-narrowing",
                     "-Xcompiler -Wno-error=maybe-uninitialized",