Bug 30203: Circulation.t: prevent locking by setting envvar

Bug 30203: Circulation.t: prevent locking by setting envvar

Running this test without prove is disastrous. The LOCK in
the called SendCirculationAlert will ruin your data.
But no longer when you apply this patch.

Test plan:
Run prove Circulation.t
Inspect your data (e.g. borrowers table).
Run perl Circulation.t
Inspect your data (e.g. borrowers table) again.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>