ENGCOM-962: [Forwardport] Fix faulty admin spinner animation #14182

 - Merge Pull Request #14182 from dimonovp/magento2:2.3-develop-PR-port-13700
 - Merged commits:
   1. 094d555

Author: magento-engcom-team

app/design/adminhtml/Magento/backend/web/css/source/variables/_spinner.less

@@ -26,4 +26,4 @@
 @spinner-rotate-step: 45;
 
 //  One step in degree
-@spinner-delay: .9;
+@spinner-delay: .9s;