Continue even if Process.setpgrp fails

In CircleCI, calling Process.setpgrp raises an "Operation not permitted" error,
but other than that flatware works.

In this change, we allow flatware to continue when the error is raised.

If flatware is executed with --log, then it will print:
INFO -- : flatware sink continuing after: Process.setpgrp: Operation not permitted

At Carwow, we have been running flatware on CircleCI for about 1 month
(with a monkey-patched Process.setpgrp) and it works great!

It allowed Carwow to reduce CircleCI credits by half, and also our Docker Hub pulls.

lib/flatware/cli.rb

@@ -55,7 +55,8 @@ def clear
 
     def start_sink(jobs:, workers:, formatter:)
       $0 = 'flatware sink'
-      Process.setpgrp
+      try_setpgrp
+
       passed = Sink.start_server(
         jobs: jobs,
         formatter: Flatware::Broadcaster.new([formatter]),
@@ -65,6 +66,12 @@ def start_sink(jobs:, workers:, formatter:)
       exit passed ? 0 : 1
     end
 
+    def try_setpgrp
+      Process.setpgrp
+    rescue Errno::EPERM => e
+      Flatware.log 'continuing after: Process.setpgrp:', e.message
+    end
+
     def workers
       options[:workers]
     end