Rakefile: Update the test task to pass on s390x CPU architecture.

This commit is a rework for the commit 9f3b9c4
that is a workaround fixing test failures on Ubuntu jammy s390x.

This commit simplifies the workaround. Read the commit message for the commit
9f3b9c4 for details of the issue.

Rakefile

@@ -1,7 +1,16 @@
 require "bundler/gem_tasks"
 require "rake/testtask"
 
-Rake::TestTask.new(:test) do |t|
+desc "Run tests"
+task :test do
+  # Avoid possible test failures with the zlib applying the following patch on
+  # s390x CPU architecture.
+  # https://github.com/madler/zlib/pull/410
+  ENV["DFLTCC"] = "0" if RUBY_PLATFORM =~ /s390x/
+  Rake::Task["test_internal"].invoke
+end
+
+Rake::TestTask.new(:test_internal) do |t|
   t.libs << "test/lib"
   t.ruby_opts << "-rhelper"
   t.test_files = FileList["test/**/test_*.rb"]