[4.0] Fix for Bug after creating an override

[astridx]

Pull Request for Issue # #19475

Summary of Changes

Set UA User agent to 'Joomla'

Testing Instructions

1. Open Extensions->Templates-> Create overrides.
2. Try any option Module, Component, Layout.
   -> an error will occur.
3. Apply this patch and open Extensions->Templates-> Create overrides.
4. Try any option Module, Component, Layout.
   -> override is created.

Expected result

Creates an override of the extension (folder+files)

Actual result

Getting this error :
0 Argument 1 passed to Joomla\CMS\Version::getUserAgent() must be of the type string, null given, called in libraries/src/Factory.php on line 758

Folder is created, no files.

Documentation Changes Required

No

[ghost]

I have tested this item ✅ successfully on a80cc0e

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/19482.}

[ghazal]

I have tested this item ✅ successfully on a80cc0e

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/19482.}

[ghost]

Ready to Commit after two successful tests.

[wilsonge]

Thanks :)