Added only one word to nextcloud migration guide (#18497)

This single word added would have helped me much during my many tries to
install nextcloud 🙈
Hopefully, if added, it will help other users.

Changed "Install with a temporary user" to "Install with a temporary
admin user".

**Description**
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⚒️ Fixes  # <!--(issue)-->

**⚙️ 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
- [x] Documentation change

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only added one word in documentation
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**✔️ Checklist:**

- [ ] ⚖️ My code follows the style guidelines of this project
- [ ] 👀 I have performed a self-review of my own code
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- [x] 📄 I have made corresponding changes to the documentation
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- [ ] 🧪 I have added tests to this description that prove my fix is
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**➕ App addition**

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- [ ] 🖼️ I have added an icon in the Chart's root directory called
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Signed-off-by: HoMS1987 <49567220+HoMS1987@users.noreply.github.com>

charts/enterprise/nextcloud/docs/migration-guide.md

@@ -81,7 +81,7 @@ The new version of Nextcloud uses apps instead of www-data for file ownership. A
 
 ## Install Nextcloud
 
-Install with a temporary user that you do not currently use for Nextcloud (ie. temp)
+Install with a temporary admin user that you do not currently use for Nextcloud (ie. temp)
 
 Setup Nextcloud UserData storage with your previous UserData dataset or the dataset you copied your UserData to.