PdfParser: Don't use list as def in read_prev_trailer

It's not recommended to use the empty list as default value in functions
or methods because Python interpreter evaluates during parsing, so it
will be the same list for different calls.

https://pylint.pycqa.org/en/latest/user_guide/messages/warning/dangerous-default-value.html

Author: danigm

src/PIL/PdfParser.py

@@ -692,7 +692,7 @@ def read_trailer(self) -> None:
             self.read_prev_trailer(self.trailer_dict[b"Prev"])
 
     def read_prev_trailer(
-        self, xref_section_offset: int, processed_offsets: list[int] = []
+        self, xref_section_offset: int, processed_offsets: list[int] = None
     ) -> None:
         assert self.buf is not None
         trailer_offset = self.read_xref_table(xref_section_offset=xref_section_offset)
@@ -708,6 +708,8 @@ def read_prev_trailer(
         )
         trailer_dict = self.interpret_trailer(trailer_data)
         if b"Prev" in trailer_dict:
+            if processed_offsets is None:
+                processed_offsets = []
             processed_offsets.append(xref_section_offset)
             check_format_condition(
                 trailer_dict[b"Prev"] not in processed_offsets, "trailer loop found"