Bump juju/testing dep to fix timeout issue in mongo tests

See juju/testing#160 for more details

Author: achilleasa

go.mod

@@ -70,7 +70,7 @@ require (
 	github.com/juju/schema v1.0.1-0.20190814234152-1f8aaeef0989
 	github.com/juju/systems v0.0.0-20200925032749-8c613192c759
 	github.com/juju/terms-client/v2 v2.0.0-20210309081804-aed8368405f6
-	github.com/juju/testing v0.0.0-20210302031854-2c7ee8570c07
+	github.com/juju/testing v0.0.0-20210324180055-18c50b0c2098
 	github.com/juju/txn v0.0.0-20210302043154-251cea9e140a
 	github.com/juju/utils v0.0.0-20200604140309-9d78121a29e0
 	github.com/juju/utils/v2 v2.0.0-20200923005554-4646bfea2ef1

go.sum

@@ -552,8 +552,9 @@ github.com/juju/testing v0.0.0-20191001232224-ce9dec17d28b/go.mod h1:63prj8cnj0t
 github.com/juju/testing v0.0.0-20200608005635-e4eedbc6f7aa/go.mod h1:hpGvhGHPVbNBraRLZEhoQwFLMrjK8PSlO4D3nDjKYXo=
 github.com/juju/testing v0.0.0-20200706033705-4c23f9c453cd/go.mod h1:hpGvhGHPVbNBraRLZEhoQwFLMrjK8PSlO4D3nDjKYXo=
 github.com/juju/testing v0.0.0-20200923013621-75df6121fbb0/go.mod h1:Ky6DwobyXXeXSqRJCCuHpAtVEGRPOT8gUsFpJhDoXZ8=
-github.com/juju/testing v0.0.0-20210302031854-2c7ee8570c07 h1:6QA3rIUc3TBPbv8zWa2KQ2TWn6gsn1EU0UhwRi6kOhA=
 github.com/juju/testing v0.0.0-20210302031854-2c7ee8570c07/go.mod h1:7lxZW0B50+xdGFkvhAb8bwAGt6IU87JB1H9w4t8MNVM=
+github.com/juju/testing v0.0.0-20210324180055-18c50b0c2098 h1:yrhek184cGp0IRyHg0uV1khLaorNg6GtDLkry4oNNjE=
+github.com/juju/testing v0.0.0-20210324180055-18c50b0c2098/go.mod h1:7lxZW0B50+xdGFkvhAb8bwAGt6IU87JB1H9w4t8MNVM=
 github.com/juju/txn v0.0.0-20190416045819-5f348e78887d/go.mod h1:ZgVptALKKa9UUv7ItEJVQjFWNG/0bs+tAu0ad0O8DAE=
 github.com/juju/txn v0.0.0-20210302043154-251cea9e140a h1:/NIvlTv1px6ct0WBa9PctsgORDTVoDYdniYeLI4kdfw=
 github.com/juju/txn v0.0.0-20210302043154-251cea9e140a/go.mod h1:7AHyL/X/p4k0qJ8oegFiI/FYMNWzMznvsHLhE346+ms=