fix: AttributeErrors from event handler move

[NeloBlivion]

Summary

Someone didn't press ctrl+f Renames extra_events to _event_handlers which caused issues during command errors and cog unloading.

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.

[codecov]

Codecov Report

Merging #1946 (973de8b) into master (34a23eb) will not change coverage.
The diff coverage is 0.00%.

❗ Current head 973de8b differs from pull request most recent head 6eea11e. Consider uploading reports for the commit 6eea11e to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1946   +/-   ##
=======================================
  Coverage   33.36%   33.36%           
=======================================
  Files          97       97           
  Lines       18851    18851           
=======================================
  Hits         6289     6289           
  Misses      12562    12562           

Flag	Coverage Δ
macos-latest-3.10	33.34% <0.00%> (ø)
macos-latest-3.11	33.34% <0.00%> (ø)
macos-latest-3.8	33.35% <0.00%> (ø)
macos-latest-3.9	33.35% <0.00%> (ø)
ubuntu-latest-3.10	33.34% <0.00%> (ø)
ubuntu-latest-3.11	33.34% <0.00%> (ø)
ubuntu-latest-3.8	33.35% <0.00%> (ø)
ubuntu-latest-3.9	33.35% <0.00%> (ø)
windows-latest-3.10	33.34% <0.00%> (ø)
windows-latest-3.11	33.34% <0.00%> (ø)
windows-latest-3.8	33.35% <0.00%> (ø)
windows-latest-3.9	33.35% <0.00%> (ø)

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Impacted Files	Coverage Δ
discord/cog.py	34.92% <0.00%> (ø)

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[Lulalaby]

I hate that update branch is enforced -.-