MessageStrip: close button does not become active on Enter

[ilhan007]

Describe the bug
When hitting Enter on the close button, the close event is fired, but the button does not become active, with Space and mouse click is fine,

To reproduce
Steps to reproduce the behavior:

1. Go to https://sap.github.io/ui5-webcomponents/master/playground/main/pages/MessageStrip/
2. Focus the close button
3. Hit Enter

Expected behavior
The close button to be in active state when the Enter key is pressed

Context

• UI5 Web Components version: master
• OS/Platform: {...} MacOS
• Browser (if relevant): {...} Chrome
• Other information: {...}