Fix: ensure sport generator produces single sport unless a number of sports is requested

[si-lens]

Summary

Fixes Issue #2608
there was a bug that resulted in Faker::Sport.sport(include_ancient: true) generating an array of sports instead of a single sport.
The problem was caused by this line.
When using << to add ancient_olympics sports to the sports array we were creating a nested array that looked like that:

      ['3x3 basketball', 'Archery', 'Artistic gymnastics', 'Artistic swimming', 'Athletics',
       'Badminton', 'Baseball', 'Basketball', 'Beach volleyball', 'BMX freestyle', 'BMX racing',
       'Boxing', 'Canoe/kayak flatwater', 'Canoe/kayak slalom', 'Diving', 'Equestrian', 'Fencing',
       'Football', 'Golf', 'Handball', 'Hockey', 'Judo', 'Karate', 'Marathon swimming', 'Modern pentathlon',
       'Mountain bike', 'Rhythmic gymnastics', 'Road cycling', 'Rowing', 'Rugby', 'Sailing', 'Shooting',
       'Skateboarding', 'Softball', 'Sport climbing', 'Surfing', 'Swimming', 'Table tennis', 'Taekwondo',
       'Tennis', 'Track cycling', 'Trampoline', 'Triathlon', 'Volleyball', 'Water polo', 'Weight lifting', 'Wrestling',
       'Alpine skiing', 'Biathlon', 'Bobsleigh', 'Cross-country', 'Curling', 'Figure skating', 'Freestyle skiing',
       'Ice hockey', 'Luge', 'Nordic combined', 'Short track speed skating', 'Skeleton', 'Ski jumping', 'Snowboard',
       'Speed skating', 'Archery', 'Athletics', 'Badminton', 'Boccia', 'Canoe', 'Cycling', 'Equestrian',
       'Football (5-a-side)', 'Goalball', 'Judo', 'Powerlifting', 'Rowing', 'Shooting', 'Sitting volleyball',
       'Swimming', 'Table tennis', 'Taekwondo', 'Triathlon', 'Wheelchair basketball', 'Wheelchair fencing',
       'Wheelchair rugby', 'Wheelchair tennis', 'Alpine skiing', 'Biathlon', 'Cross-country skiing',
       'Para ice hockey', 'Snowboard', 'Wheelchair curling',
       ['Boxing', 'Chariot racing', 'Discus', 'Horse racing', 'Long jump', 'Pankration', 'Pentathlon', 'Running', 'Wrestling']]

So once in a while, this last element was picked by the .sample method and caused the problem.

I changed the sport method to use concat method to combine arrays correctly.

Other Information

[si-lens]

In docs it states:
Only refactoring and documentation changes require no new tests. If you are adding functionality or fixing a bug, we need a test! We use [Minitest](https://github.com/seattlerb/minitest) in this project.
And I am not really sure whether I should write a test for that. If so, what kind of test would you like to have to cover it?

[thdaraujo]

nice catch, thank you!