Set store=False as default in load_extension(s)

[NeloBlivion]

Makes store=False the default in load_extension/load_extensions, which keeps the behaviour inline with previous versions.

Summary

With #1423, extension loading was reworked to allow loading entire folders at once. This is a very convenient addition, however it introduced the store kwarg which decides whether load_extension will raise an error or not if a cog fails to load.

In the past load_extension has always raised an error when this happens, however with this PR the default has been set as store=True, which instead stores the error in a dict for the user to parse themselves. While this technically isn't a breaking change since it still functions, the behaviour is different enough from before to cause confusion with users who updated: without setting the store kwarg, cogs that have errors will appear to load correctly if you haven't accounted for the change. Neither was this change made note of at all in any update notes.

As such, I believe it'd be more appropriate for store=False to be the default to be inline with previous behaviorr.

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.

[baronkobama]

Good idea, LGTM.

[EmmmaTech]

k