[6.0] Adapter should have in install routine always the current manifest

[laoneo]

Summary of Changes

When updating two extension at the same time, then files from the first extension are copied to the second one because of caching an adapter instance. Relevant pr is #43792.

Testing Instructions

• Install two older versions of a plugin which have an update site or install two free ones from DPCalendar like this and this).
• Open /administrator/index.php?option=com_installer&view=update and click on "Check for updates"
• Select the two plugins and hit the "Update" button

BEFORE DOING THE SECOND TEST WITH THE PATCH, UNINSTALL THE EXTENSIONS FIRST!

Actual result BEFORE applying this Pull Request

One folder, where the plugin is installed to, contains its own manifest file only. The other contains it's own manifest file and the one from the other plugin.

Expected result AFTER applying this Pull Request

Both plugin installation folders do only contain their own installable files.

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

[dautrich]

I have tested this item ✅ successfully on 27f31ef

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[mariantanase]

I have tested this item ✅ successfully on 27f31ef

The behavior is as described.

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Before:

After:

[tecpromotion]

RTC

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[softforge]

Thank you @laoneo for the pr and the test instructions. Thank you testers and all involved in getting this release blocker in