[5.0] fix joomla update not download url

[heelc29]

Summary of Changes

property downloadurl is protected since #41118 by @alikon

so the check fails here now

joomla-cms/administrator/components/com_joomlaupdate/src/View/Joomlaupdate/HtmlView.php

Line 177 in 3fa34be

$hasDownload = isset($this->updateInfo['object']->downloadurl->_data);

Testing Instructions

enter Custom URL for joomla update, for eg. of this pull request

click on joomla update quickicon which shows that an update is available

Actual result BEFORE applying this Pull Request

Expected result AFTER applying this Pull Request

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[alikon]

I have tested this item ✅ successfully on 2ddec12

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/41364.}

[HLeithner]

Thanks