Alter fix from merged PR

Author: exodist

t/regression/291-async-subtest-done-testing.t

@@ -1,10 +1,6 @@
 use Test2::V0;
 
-BEGIN {
-    require Config;
-    skip_all('no fork')
-        unless ($Config::Config{d_fork} or $Config::Config{d_pseudofork});
-}
+use Test2::Require::RealFork;
 
 use Test2::Tools::AsyncSubtest qw/fork_subtest/;