Avoid D301 autofix for u prefixed strings (#8495)

This PR avoids creating the fix for `D301` if the string is prefixed
with `u` i.e., it's a unicode string. The reason being that `u` and `r`
cannot be used together as it's a syntax error.

Refer:
https://github.com/astral-sh/ruff/issues/8402#issuecomment-1788783287

crates/ruff_linter/resources/test/fixtures/pydocstyle/D301.py

@@ -31,3 +31,7 @@ def make_unique_pod_id(pod_id: str) -> str | None:
     :param pod_id: requested pod name
     :return: ``str`` valid Pod name of appropriate length
     """
+
+
+def shouldnt_add_raw_here2():
+    u"Sum\\mary."