chore(deps): update dependency slather to v2.8.4 (#390)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [slather](https://redirect.github.com/SlatherOrg/slather) | `2.8.3` -> `2.8.4` | [![age](https://developer.mend.io/api/mc/badges/age/rubygems/slather/2.8.4?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/rubygems/slather/2.8.4?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/rubygems/slather/2.8.3/2.8.4?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/rubygems/slather/2.8.3/2.8.4?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>SlatherOrg/slather (slather)</summary>

### [`v2.8.4`](https://redirect.github.com/SlatherOrg/slather/blob/HEAD/CHANGELOG.md#v284)

[Compare Source](https://redirect.github.com/SlatherOrg/slather/compare/v2.8.3...v2.8.4)

-   Don't crash when 0% coverage is causing empty JSON
    [jarrodlombardo-EventBase](https://redirect.github.com/jarrodlombardo-EventBase)
    [#&#8203;570](https://redirect.github.com/SlatherOrg/slather/pull/570)

-   Xcode 16 compatibility (as of beta 5)
    [ksuther](https://redirect.github.com/ksuther)
    [#&#8203;568](https://redirect.github.com/SlatherOrg/slather/pull/568)

</details>

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### Configuration

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♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

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

---

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Gemfile.lock

@@ -5,7 +5,7 @@ GEM
       base64
       nkf
       rexml
-    activesupport (7.1.3.4)
+    activesupport (7.1.4)
       base64
       bigdecimal
       concurrent-ruby (~> 1.0, >= 1.0.2)