Plugin Manager has problems with plugin.xml files after Updateing to 5.7.21

[jhit]

Description

After updateing to what will be the next version 5.7.21 I got multiple issues with the Plugin Manager:

First Problem

Unable to parse file "/var/www/clients/client1/web1/web/stage/custom/plugins/NetzpContentBuilder/plugin.xml". Message: [ERROR 1871] Element 'support': This element is not expected. (in /var/www/clients/client1/web1/web/stage/ - line 14, column 0)
and
Unable to parse file "/var/www/clients/client1/web1/web/stage/custom/plugins/CompraCacheWarmUp/plugin.xml". Message: [ERROR 1871] Element 'supplier': This element is not expected. (in /var/www/clients/client1/web1/web/stage/ - line 7, column 0)

The problematic code in the XML is like:

<support>http://shopwareplugins.de/support</support>
<supplier>myplugin GmbH</supplier>

both <supplier> and <support> do not validate with the provided XSD file in the shop in "../../../engine/Shopware/Components/Plugin/schema/plugin.xsd"

Second problem

After removing the <support> tag from all plugin.xml files I got another error from the Extension Manager:
Unable to parse file "/var/www/clients/client1/web1/web/stage/custom/plugins/SwagEmotionAdvanced/plugin.xml". Message: [ERROR 1843] Element 'changelog': Character content other than whitespace is not allowed because the content type is 'element-only'. (in /var/www/clients/client1/web1/web/stage/ - line 123, column 0)

Parsing the <changelog version=""> Tags fails.

PHP Version

7.4

Shopware Version

5.7.21

How to reproduce

Install latest update build and go to Extension manager. If you have some older Plugins with an <support> element in the plugin.xml you will get this error.
Otherwise add the element to any other plugin to trigger the error.

Expected behaviour

Shopware version 5.7.20 had no issues with this. So I would expect this should not cause issues in 5.7.21

Actual behaviour

Getting a black message bubble with error message.