Harden the test against flickering.

I found it was passing in isolation but failing
when run with the whole suite, depending on when
it runs.  It's best to make it relative to the
current memory usage of the process.

spec/integration/middleware/memory_usage_monitor_spec.rb

@@ -64,15 +64,15 @@ def self.puts(msg)
 
           stub_const('BloatedJobClass', bloated_job_class)
 
-          [25, 60, 25].each do |target_mb|
-            queue.put(BloatedJobClass, { target: target_mb * (1_000) })
+          max_memory = (MemoryUsageMonitor.current_usage_in_kb * 1.5).to_i
+
+          [(max_memory / 2), (max_memory * 1.1).to_i, (max_memory / 2)].each do |target|
+            queue.put(BloatedJobClass, { target: target })
           end
 
           job_records = []
 
-          worker.extend(Qless::Middleware::MemoryUsageMonitor.new(
-            max_memory: 50_000
-          ))
+          worker.extend(MemoryUsageMonitor.new(max_memory: max_memory))
 
           run_worker_concurrently_with(worker) do
             3.times do