Flaky test: `TestLeakyBucketGregorian`

[miparnisari]

=== RUN   TestLeakyBucketGregorian/third_hit;_leak_one_hit
    functional_test.go:657: 
        	Error Trace:	/home/runner/work/gubernator/gubernator/functional_test.go:657
        	Error:      	Not equal: 
        	            	expected: 58
        	            	actual  : 59
        	Test:       	TestLeakyBucketGregorian/third_hit;_leak_one_hit

Seen in https://github.com/mailgun/gubernator/actions/runs/6807157074/job/18509537658?pr=200