add test that ;secure Set-Cookie header doesn't affect previous cookie's value
The Ignore name- and value-less Set-Cookie: ; bar test was also failing
before, but due to bug 1848226 it wasn't removed in bug 1892748.
Differential Revision: https://phabricator.services.mozilla.com/D213551
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1901325
gecko-commit: a60507c6dfe7fff34a6fd90d21f5cc9a5eb21f06
gecko-reviewers: edgul