Correct cookie expiry format string

"Mon, 29-Jul-24 04:52:08 GMT" is parsed as Just 0024-07-29 04:52:08 UTC
instead of 2024.

This small change seems to fix the problem.

From Date.Time.Format haddock (not very clear)
%Y
year, no padding. Note %0y and %_y pad to four chars
%y
year of century, 0-padded to two chars, 00 - 99
...
In the absence of %C or %Y, century is 1969 - 2068.