Prior to this commit, MockCookie.parse() failed with an
IllegalArgumentException when attempting to parse a custom attribute
with a value, such as "Version=1". This is a regression that was
inadvertently introduced in 7fc4937199
when adding support for the "Partitioned" attribute which does not
support a value.
This commit addresses this regression by parsing both the name and the
value from an optional, custom attribute.
See gh-31454
Closes gh-34575
020f556841