- Update the requirements, add note about test suite

- Update to version 5.3.1.
* New features
* Add a toolbar to the Variable Explorer viewer for dictionaries,
lists and sets to easily access the functionality available
through its context menu.
* Add navigation with extra buttons in the editor for mouses
that support them.
* Add --no-web-widgets command line option to disable
plugins/widgets that use Qt Webengine widgets.
* Important fixes
* Fix several important bugs related to the Autoformat on save
functionality.
* Fix options related to the Working directory entry in Preferences.
* Make code completion widget entries accessible to screen readers.
* New API features
* Add get_command_line_options to SpyderPluginV2 so that
plugins can access the command line options passed to Spyder.
* The current interpreter used by all Spyder plugins can be
accessed now through the executable option of the Main \
interpreter plugin.
* Full changelog here,
* https://github.com/spyder-ide/spyder/releases/tag/v5.3.1 (forwarded request 980901 from bnavigator)