Fix Sidekiq process group killing

lib/gitlab/sidekiq_signals.rb

@@ -35,8 +35,11 @@ module Gitlab
     # signals from outside the process group, but that isn't fatal.
     def self.blindly_signal_pgroup!(signal)
       old_trap = trap(signal, 'IGNORE')
-      Process.kill(signal, "-#{Process.getpgrp}")
-      trap(signal, old_trap)
+      begin
+        Process.kill(signal, 0)
+      ensure
+        trap(signal, old_trap)
+      end
     end
   end
 end

spec/lib/gitlab/sidekiq_signals_spec.rb

@@ -44,7 +44,7 @@ describe Gitlab::SidekiqSignals do
 
           expect(Process)
             .to receive(:kill)
-            .with(signal, "-#{Process.pid}")
+            .with(signal, 0)
             .ordered
 
           expect(described_class)