Skip tests that fail due to Ruby bug 14060 on Ruby 2.4.4.

On Ruby 2.4.4 in safe mode, require will fail with a SecurityError for
any file that has not previously been loaded, regardless of whether the
file name is tainted.

See https://bugs.ruby-lang.org/issues/14060#note-5

Failing test job:
https://travis-ci.org/tzinfo/tzinfo/jobs/422745006

(cherry picked from commit ed162f3)

test/tc_ruby_data_source.rb

@@ -55,6 +55,8 @@ def test_load_timezone_info_minus
   end
 
   def test_load_timezone_info_tainted
+    skip_if_has_bug_14060
+
     safe_test do
       identifier = 'Europe/Amsterdam'.dup.taint
       assert(identifier.tainted?)
@@ -65,6 +67,8 @@ def test_load_timezone_info_tainted
   end
 
   def test_load_timezone_info_tainted_and_frozen
+    skip_if_has_bug_14060
+
     safe_test do
       info = @data_source.load_timezone_info('Europe/Amsterdam'.dup.taint.freeze)
       assert_equal('Europe/Amsterdam', info.identifier)

test/tc_timezone.rb

@@ -261,6 +261,8 @@ def test_get_tainted_and_frozen_loaded
   end
 
   def test_get_tainted_not_previously_loaded
+    skip_if_has_bug_14060
+
     safe_test do
       identifier = 'Europe/Andorra'.dup.taint
       assert(identifier.tainted?)
@@ -271,6 +273,8 @@ def test_get_tainted_not_previously_loaded
   end
 
   def test_get_tainted_and_frozen_not_previously_loaded
+    skip_if_has_bug_14060
+
     safe_test do
       tz = Timezone.get('Europe/Amsterdam'.dup.taint.freeze)
       assert_equal('Europe/Amsterdam', tz.identifier)

test/test_utils.rb

@@ -96,6 +96,16 @@ def safe_test(options = {})
       thread.join
     end
   end
+
+  def skip_if_has_bug_14060
+    # On Ruby 2.4.4 in safe mode, require will fail with a SecurityError for
+    # any file that has not previously been loaded, regardless of whether the
+    # file name is tainted.
+    # See https://bugs.ruby-lang.org/issues/14060#note-5.
+    if RUBY_ENGINE == 'ruby' && RUBY_VERSION == '2.4.4'
+      skip('Skipping test due to Ruby 2.4.4 being affected by Bug 14060 (see https://bugs.ruby-lang.org/issues/14060#note-5)')
+    end
+  end
 
   def assert_array_same_items(expected, actual, msg = nil)
     full_message = message(msg, '') { diff(expected, actual) }