TestCompactFlushQueuedMemTableAndFlushMetrics flaky on windows

[jbowens]

https://github.com/cockroachdb/pebble/runs/6203219476?check_suite_focus=true

 === RUN   TestCompactFlushQueuedMemTableAndFlushMetrics
    assertion_compare.go:230: 
        	Error Trace:	compaction_test.go:3002
        	            				compaction_test.go:3011
        	Error:      	"50000" is not less than "0"
        	Test:       	TestCompactFlushQueuedMemTableAndFlushMetrics
        	Messages:   	[]
--- FAIL: TestCompactFlushQueuedMemTableAndFlushMetrics (0.01s)

[nicktrav]

In the words of DJ Khaled: "Another one!":
https://github.com/cockroachdb/pebble/runs/6214168198?check_suite_focus=true

[nicktrav]

https://github.com/cockroachdb/pebble/runs/6845246075?check_suite_focus=true

[nicktrav]

https://github.com/cockroachdb/pebble/runs/7116117118?check_suite_focus=true

[nicktrav]

https://github.com/cockroachdb/pebble/runs/7587273080?check_suite_focus=true