Fix flake8 D301 Use r""" if any backslashes in a docstring

Author: rodrigobnogueira

tests/test_cookie_helpers.py

@@ -1163,7 +1163,7 @@ def test_parse_set_cookie_headers_ctl_chars_from_octal(
 
 
 def test_parse_set_cookie_headers_literal_ctl_chars() -> None:
-    """Ensure literal control characters in a cookie value don't crash the parser.
+    r"""Ensure literal control characters in a cookie value don't crash the parser.
 
     If the raw header itself contains a control character (e.g. BEL \\x07),
     both the decoded value and coded_value are unsalvageable.  The parser
@@ -1650,7 +1650,7 @@ def test_parse_cookie_header_empty_key_in_fallback(
 
 
 def test_parse_cookie_header_literal_ctl_chars() -> None:
-    """Ensure literal control characters in a cookie value don't crash the parser.
+    r"""Ensure literal control characters in a cookie value don't crash the parser.
 
     If the raw header itself contains a control character (e.g. BEL \\x07),
     the cookie is unsalvageable.  The parser should gracefully skip it.