CLC-4005 Filter task update requests

QA version of https://github.com/ets-berkeley-edu/calcentral/pull/2729

Note that this does *not* include @christianv's front-end fix: https://github.com/ets-berkeley-edu/calcentral/pull/2725
This will make it easier to QA the server-side fix, which is also more important. We can land the client-side later.