Fix reports bug

Look like this bug was introduced here:
https://github.com/dimagi/commcare-hq/commit/1c045d697976cbf9fe854ce7c8d9cd2ebe16b6c4#diff-e41763d8d0b6724fd2a313c6f2caa85eL58

@czue I didn't test this extensively because I'm assuming the list was changed to a tuple by mistake. Does that sound right?