Migrate fa-spinner to spinner in views dashboard todos.
What does this MR do?
Migrates the use of .fa-spinner icons to .spinner ones where previously icon('spinner spin')  was used in app/views/dashboard/todos. See #202601 (closed)
This is in WIP state because the SCSS changes introduced also affect an ee feature; i.e. .btn-loading class is used in /ee/app/views/shared/members/ee/_override_member_buttons.html.haml on line 21. The use of icon('spinner spin')  (see line 24) should be changed to the new %i.spinner approach.
@blabuschagne please advise on how to proceed.
NOTE: I was not able to test this on IE11 and Edge as I am on Mac and the current tools I have for testing are not working with my local setup.
Screenshots
Chrome
Safari
Firefox
Does this MR meet the acceptance criteria?
Conformity
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Changelog entry 
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Documentation (if required) 
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Code review guidelines 
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Merge request performance guidelines 
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Style guides 
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Database guides 
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Separation of EE specific content 
Availability and Testing
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Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process. 
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Tested in all supported browsers 
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Informed Infrastructure department of a default or new setting change, if applicable per definition of done 
Security
If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:
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Label as security and @ mention @gitlab-com/gl-security/appsec
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The MR includes necessary changes to maintain consistency between UI, API, email, or other methods 
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Security reports checked/validated by a reviewer from the AppSec team 


