fix "method redefined"

[kenchan]

I fixed it because the following warning appears when running it with Ruby 3.3.

❯ bundle exec rake
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/core_ext/hash.rb:2: warning: method redefined; discarding old slice
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/configurable.rb:50: warning: method redefined; discarding old slack_team
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/configurable.rb:54: warning: method redefined; discarding old slack_team=
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/configurable.rb:63: warning: method redefined; discarding old slack_token
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/userable.rb:5: warning: method redefined; discarding old users
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/userable.rb:15: warning: method redefined; discarding old guests
/home/kenchan/src/github.com/pepabo/arisaid/lib/arisaid/userable.rb:25: warning: method redefined; discarding old bots
Run options: --seed 45432

# Running:

............

Finished in 0.074746s, 160.5428 runs/s, 280.9499 assertions/s.

12 runs, 21 assertions, 0 failures, 0 errors, 0 skips