Fix some typos in admin filemanager

[matks]

Questions	Answers
Branch?	develop
Description?	Fix some typos in admin filemanager
Type?	improvement
Category?	BO
BC breaks?	no
Deprecations?	no
Fixed ticket?
How to test?	No need for QA

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This change is 

[prestonBot]

Hi, thanks for this contribution!

I found some issues with the Pull Request description:

• Your pull request does not seem to fix any issue, consider creating one (see note below) and linking it by writing Fixes #1234.

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[Progi1984]

Thanks @matks