test: get to passing on JRuby

- update error message
- avoid race condition on cookie expiration

test/helper.rb

@@ -50,6 +50,6 @@ end
 
 def sleep_until(time)
   if (s = time - Time.now) > 0
-    sleep s
+    sleep s + 0.01
   end
 end

test/test_http_cookie_jar.rb

@@ -10,10 +10,8 @@ module TestHTTPCookieJar
     end
 
     def test_nonexistent_store_in_config
-      assert_raise_with_message(
-        ArgumentError,
-        /cookie store unavailable: :nonexistent, error: cannot load .*nonexistent_store/
-      ) {
+      expected = /cookie store unavailable: :nonexistent, error: (cannot load|no such file to load) .*nonexistent_store/
+      assert_raise_with_message(ArgumentError, expected) {
         HTTP::CookieJar.new(store: :nonexistent)
       }
     end