docs(authelia): fix trusted headers (truecharts#18740)

**Description**
Fix trusted headers section.

⚒️ Fixes  # 

**⚙️ Type of change**

- [ ] ⚙️ Feature/App addition
- [ ] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code

**🧪 How Has This Been Tested?**

**📃 Notes:**

**✔️ Checklist:**

- [ ] ⚖️ My code follows the style guidelines of this project
- [ ] 👀 I have performed a self-review of my own code
- [ ] #️⃣ I have commented my code, particularly in hard-to-understand
areas
- [ ] 📄 I have made corresponding changes to the documentation
- [ ] ⚠️ My changes generate no new warnings
- [ ] 🧪 I have added tests to this description that prove my fix is
effective or that my feature works
- [ ] ⬆️ I increased versions for any altered app according to semantic
versioning

**➕ App addition**

If this PR is an app addition please make sure you have done the
following.

- [ ] 🖼️ I have added an icon in the Chart's root directory called
`icon.png`

---

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charts/enterprise/authelia/docs/Setup-Guide.md

@@ -98,7 +98,7 @@ Please see [Authelia Rules](./authelia-rules) for more advanced rules.
 - Check `trustForwardHeader`
 - Add the following `authResponseHeaders` (press `Add` 4 times)
   - `Remote-User`
-  - `Remote-Group`
+  - `Remote-Groups`
   - `Remote-Name`
   - `Remote-Email`