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.

Author: pixeltrix

app/models/invalidation.rb

@@ -166,13 +166,15 @@ def invalidate!
       counted_at: Time.current
     )
 
-    matching_signatures.find_in_batches(batch_size: 100) do |signatures|
-      signatures.each do |signature|
-        signature.invalidate!(Time.current, self)
-        increment!(:invalidated_count)
+    Appsignal.without_instrumentation do
+      matching_signatures.find_in_batches(batch_size: 100) do |signatures|
+        signatures.each do |signature|
+          signature.invalidate!(Time.current, self)
+          increment!(:invalidated_count)
+        end
+
+        reload and return if cancelled?
       end
-
-      reload and return if cancelled?
     end
 
     update(completed_at: Time.current)