fix(test): add 500ms timeout after deleting a collection

[prabalsingh24]

Problem

One test was inconsistent and showing false negative. Adding timeout after deleting a collection will make sure that ES index is updated

Solution

wait 500ms after deleting a collection to make sure ES index is updated

Areas of Impact

test/src/server/routes/collection.js

[MonkeyDo]

👌 Thank you !

[coveralls]

Coverage increased (+0.07%) to 60.976% when pulling 39434bb on prabalsingh24:add-timeout-in-test into a450600 on bookbrainz:master.