[1.x] fix: change length of email field

[DavideIadeluca]

1.x pendent to #4118

Fixes #0000
It appears as if the email validator allows 254 chars for the entire email, while the DB field only allows 150. This results in email addresses simply being truncated without any error message when creating users with longer email addresses.

Changes proposed in this pull request:
Increase length of email field to 254 chars to match the validator

Reviewers should focus on:
See https://www.rfc-editor.org/errata/eid1690

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)

[imorland]

Looks all good to me.

I think for the tests, we only really need test the longest valid and assert that longer fails. Testing the local and domain parts feels like it's unnecessary and we're just testing the validator, which should already be done in Laravel?

Anyhow, I'm happy overall here, good job!