Make sure the fake schedule is a tibble

[mrcaseb]

Fixes this error

s <- nflseedR::simulate_nfl(2024, simulations = 2)
#> ℹ 17:21:34 | Loading games data
#> ℹ No actual schedule exists for 2024, using fake schedule with correct opponents.
#> ℹ 17:21:36 | Beginning simulation of 2 seasons in 1 round
#> Error:
#> ℹ In index: 1.
#> Caused by error in `simulate_week()`:
#> ! During Week 1, your `process_games()` function had the following issues: `games` was not a tibble.

^{Created on 2024-01-19 with reprex v2.1.0}