tests: Stop reusing a variable name.
tests: Stop reusing a variable name.

`loopworker_sleep_mock` is a file-level variable used to mock out the
sleep() call in LoopQueueProcessingWorker; don't reuse the variable
name for something else.

rht/zulip,punchagan/zulip,rht/zulip,showell/zulip,zulip/zulip,kou/zulip,andersk/zulip,kou/zulip,punchagan/zulip,rht/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,showell/zulip,hackerkid/zulip,zulip/zulip,showell/zulip,eeshangarg/zulip,andersk/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,punchagan/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,punchagan/zulip,kou/zulip,showell/zulip,showell/zulip,punchagan/zulip,rht/zulip,kou/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip