Disable Appsignal monitoring when invalidating signatures
Disable Appsignal monitoring when invalidating signatures

For the same reasons as #384 we should disable the Appsignal monitoring
so that we don't use large amounts of memory when iterating over a job
that invalidates hundreds of thousands or even millions of signatures.

StatesOfJersey/e-petitions,alphagov/e-petitions,unboxed/e-petitions,unboxed/e-petitions,joelanman/e-petitions,StatesOfJersey/e-petitions,oskarpearson/e-petitions,StatesOfJersey/e-petitions,oskarpearson/e-petitions,unboxed/e-petitions,alphagov/e-petitions,oskarpearson/e-petitions,alphagov/e-petitions,unboxed/e-petitions,joelanman/e-petitions,alphagov/e-petitions,joelanman/e-petitions,StatesOfJersey/e-petitions