fix(deps): update module github.com/mailgun/mailgun-go/v4 to v4.12.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/mailgun/mailgun-go/v4	require	minor	v4.11.1 -> v4.12.0

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Release Notes

mailgun/mailgun-go (github.com/mailgun/mailgun-go/v4)

### [`v4.12.0`](https://togithub.com/mailgun/mailgun-go/releases/tag/v4.12.0) [Compare Source](https://togithub.com/mailgun/mailgun-go/compare/v4.11.1...v4.12.0) #### What's Changed - mailingListResponse incorrectly set to 'member' instead of 'list' by [@​thrawn01](https://togithub.com/thrawn01) in [https://github.com/mailgun/mailgun-go/pull/316](https://togithub.com/mailgun/mailgun-go/pull/316) **Full Changelog**: https://github.com/mailgun/mailgun-go/compare/v4.11.1...v4.12.0

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Configuration

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (27e4991) 74.10% compared to head (fb3a1ff) 74.10%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #766 +/- ## ======================================= Coverage 74.10% 74.10% ======================================= Files 44 44 Lines 1572 1572 ======================================= Hits 1165 1165 Misses 307 307 Partials 100 100 ```

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