[3.15] gh-141510: Update marshal module comment with frozendict support (GH-153655) (#153681)

gh-141510: Update `marshal` module comment with `frozendict` support (GH-153655)
(cherry picked from commit 37571ea)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Python/marshal.c

@@ -1,8 +1,8 @@
 
 /* Write Python objects to files and read them back.
    This is primarily intended for writing and reading compiled Python code,
-   even though dicts, lists, sets and frozensets, not commonly seen in
-   code objects, are supported.
+   even though dicts and frozendicts, lists, sets and frozensets,
+   not commonly seen in code objects, are supported.
    Version 3 of this protocol properly supports circular links
    and sharing. */