Update dependency mailgun.js to v10.4.0 (#21957)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [mailgun.js](https://redirect.github.com/mailgun/mailgun.js) |
[`10.3.0` ->
`10.4.0`](https://renovatebot.com/diffs/npm/mailgun.js/10.3.0/10.4.0) |
[![age](https://developer.mend.io/api/mc/badges/age/npm/mailgun.js/10.4.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/npm/mailgun.js/10.4.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/npm/mailgun.js/10.3.0/10.4.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/mailgun.js/10.3.0/10.4.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>mailgun/mailgun.js (mailgun.js)</summary>

###
[`v10.4.0`](https://redirect.github.com/mailgun/mailgun.js/blob/HEAD/CHANGELOG.md#1040-2024-12-30)

[Compare
Source](https://redirect.github.com/mailgun/mailgun.js/compare/v10.3.0...ffb37a53371756c36abdfdadac27309051f3cebf)

##### Features

- Add support for metrics
([de16ccd](de16ccd9b8))

##### Other changes

- Add tests
([78f9990](78f9990fe6))
- Update readme
([a724689](a7246892a2))

</details>

---

### Configuration

📅 **Schedule**: Branch creation - "* * * * 1-5" (UTC), Automerge - At
any time (no schedule defined).

🚦 **Automerge**: Enabled.

♻ **Rebasing**: Never, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
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ghost/mailgun-client/package.json

@@ -29,6 +29,6 @@
     "@tryghost/metrics": "1.0.34",
     "form-data": "4.0.0",
     "lodash": "4.17.21",
-    "mailgun.js": "10.3.0"
+    "mailgun.js": "10.4.0"
   }
 }

yarn.lock

@@ -22812,10 +22812,10 @@ magic-string@^0.30.0, magic-string@^0.30.1:
   dependencies:
     "@jridgewell/sourcemap-codec" "^1.4.15"
 
-mailgun.js@10.3.0:
-  version "10.3.0"
-  resolved "https://registry.yarnpkg.com/mailgun.js/-/mailgun.js-10.3.0.tgz#7599600a4c144e4df63675ede48de8fe9b38dbfc"
-  integrity sha512-HJPmninRDGlzs8izNyfM/hbvefz6ol1gqeZ+doiumEHli7kGCrLlK6hURsq6oLjDoTNwgS37CUDhBPQy7x5PeQ==
+mailgun.js@10.4.0:
+  version "10.4.0"
+  resolved "https://registry.yarnpkg.com/mailgun.js/-/mailgun.js-10.4.0.tgz#8b6221e0f1172248a487e7bfa156471058efe4dd"
+  integrity sha512-YrdaZEAJwwjXGBTfZTNQ1LM7tmkdUaz2NpZEu7+zULcG4Wrlhd7cWSNZW0bxT3bP48k5N0mZWz8C2f9gc2+Geg==
   dependencies:
     axios "^1.7.4"
     base-64 "^1.0.0"