So is there any procedure for News entries for bugfixes that need to be backported to older versions of CPython?

I would suggest the following fixup to make this work on BE (mtime is always LE, regardless of the host endianness):

--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -725,7 +725,7 @@ def test_issue112346(self):
         for mtime in (0, 42):
             with self.subTest(mtime=mtime):
                 compress = gzip.compress(data1, compresslevel=1, mtime=mtime)
-                assert struct.unpack("IxB", compress[4:10]) == (mtime, 255)
+                assert struct.unpack("<IxB", compress[4:10]) == (mtime, 255)
 
     def test_decompress(self):
         for data in (data1, data2):

Thanks for the suggestion @iii-i . That was an oversight on my part. I am going to pin in the hope this fix gets noticed.

ping

Ping @gpshead . Could you shine your light on this? It's only a very small change and it has remained under the radar for almost half a year now.

Thanks for reviewing this so quickly @serhiy-storchaka . I added a news entry.

I suggest not making this change given how long it has been the behavior of released Pythons. We cannot backport this to 3.11 as it is not a security issue. And anyone picking a change like this up in a patch release is just as likely to run into problems with the behavior change between differing Python versions.

@gpshead That makes sense. Sorry, I went into panic mode when code changes I made gave someone some reproducibility troubles.
I do hope that the two separate code paths do not cause any more in the future.