Fix "Perform all updates" task was incorrectly marked as completed

[ilicfilip]

I noticed that sometimes "Perform all updates" is marked as completed, although I haven't updated plugins.
Sometimes also "update counter" (next to the Plugins in the Dashboard menu) was missing, then on page re-load it appeared.

This indicated that some transient probably isn't not set in time and after investigation I found that it happens after the plugin is installed through the WP Dashboard (Add plugin screen). It doesnt happen on plugin update, deactivate or delete.

update_plugins transient, from which wp_get_update_data actually gets data is set on admin_init (with default priority), so that is the reason why evaluate_tasks method is bumped to that hook.
Also during the install process several AJAX requests are fired, strangely not all of them fire admin_init hook and that is the reason why \wp_doing_ajax() is added.

[github-actions]

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