Better skipping of more tests requiring fork()

See also 6cda6a94c3.
Specify the default Perl::Critic configuration

Without this, Perl::Critic will search for a .perlcriticrc file in the
user's home directory or via the PERLCRITIC environment variable (in the
absence of our own one in the current directory), which may cause test
failures (as seen on CPAN Testers) if a non-default policy configuration
is set.