Bug 33967: Add unit test to ensure SetEnv doesn't compromise $env

Bug 33967: Add unit test to ensure SetEnv doesn't compromise $env

This patch includes a unit test which checks the memory address
of the $env hashref in middlewares before and after
Koha::Middleware::Env is applied.

It succeeds when the same $env is maintained before and after
this middleware. It fails if the $env has been overwritten with
a new hashref (as evidenced by the new memory address for the
hash).

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>