[6.0] Fix fatal error on templates management

[joomdonation]

Pull Request for Issue # .

Summary of Changes

Currently, on Joomla 6.0-dev, if you access to System -> Site Templates you will get fatal error. This PR fixes that error

Testing Instructions

• Use Joomla 6.0 nightly build
• Login to administrator area of your site
• Access to System -> Site Templates

Actual result BEFORE applying this Pull Request

• You got fatal error
• You cannot access to template detail, also fatal error

Expected result AFTER applying this Pull Request

• No fatal error when access to Site Templates
• No fatal error when access to a template details

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[exlemor]

I have tested this item ✅ successfully on eca4ccd

Nice and quick check - I have successfully tested this PR!

Thank you @joomdonation.

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[krishnaGandhi11]

I have tested this item ✅ successfully on eca4ccd

Tested successfully @joomdonation :)

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/45198.}

[QuyTon]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/45198.}