fixed conference collapse/expanding reading
fixed conference collapse/expanding reading

Fixed the way screen reader reads the collapsed
and expanding of the new conferences and concluded
conferences reading.

fixes CNVS-21775

test plan:
- Go to the conferences page
- with screen reader on navigate to the
  new conferences header
- collapse and expand it notice the correct reading
- repeat above for concluded conferences
- repeat above for all screenreaders

Change-Id: I72dd37aef3410435b8326c1c99736889c8bad268
Reviewed-on: https://gerrit.instructure.com/59530
Reviewed-by: Jonathan Featherstone <c99460343437e667b0585ea68fd7caf7bd0a02ab@instructure.com>
Tested-by: Jenkins
QA-Review: Heath Hales <8ca81b68c7e2592ac614bd07f22fcc735ca55f93@instructure.com>
Product-Review: Peyton Craighill <b6cfaee6364b0ff4306081e7e83cf8ccde7c2fba@instructure.com>

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