groups_spec.rb: get rid of limit on macOS

* spec/ruby/core/process/groups_spec.rb: on macOS, getgroups(2)
  has a variant which has no limit but not setgroups(2).  so the
  default groups may exceed the limit.  as the call of setgroups
  is expected to fail here, the content does not matter.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62547 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/core/process/groups_spec.rb

@@ -53,9 +53,8 @@ describe "Process.groups=" do
 
       platform_is_not :aix do
         it "raises Errno::EPERM" do
-          groups = Process.groups
           lambda {
-            Process.groups = groups
+            Process.groups = [0]
           }.should raise_error(Errno::EPERM)
         end
       end