update ManageOutcomesFooter to provide valid background

flag=none

test plan:
  - specs pass

qa risk: low

Change-Id: Iddf3b7be0ae7b04a8e93b47786df46c125aea34d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/274128
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Omar Soto-Fortuño <omar.soto@instructure.com>
QA-Review: Omar Soto-Fortuño <omar.soto@instructure.com>
Product-Review: Omar Soto-Fortuño <omar.soto@instructure.com>

jest/jest-setup.js

@@ -59,7 +59,6 @@ const ignoredErrors = [
   /Function components cannot be given refs/,
   /Functions are not valid as a React child/,
   /invalid messageType: (notSupported|undefined)/,
-  /Invalid prop `background` of value `` supplied to `View`, expected one of/,
   /Invalid prop `children` of type `array` supplied to `Transition`/,
   /Invalid prop `children` supplied to `(Option|View)`/,
   /Invalid prop `conversation._id` of type `number` supplied to `ComposeModalManager`/,

ui/features/outcome_management/react/Management/ManageOutcomesFooter.js

@@ -63,7 +63,7 @@ const ManageOutcomesFooter = ({
       <View
         as="div"
         padding={isMobileView ? 'small' : '0'}
-        background={isMobileView ? 'secondary' : ''}
+        background={isMobileView ? 'secondary' : undefined}
       >
         <Flex
           justifyItems="space-between"