Fix test `TestOutputSizeP2SH` in `fee_test.go`

[renan061]

Describe the Issue One of the unit tests is failing non-deterministically (very rare).

fee_test.go:432: 
    	Error Trace:	/node/zetaclient/chains/bitcoin/common/fee_test.go:432
      	Error:      	Not equal: 
       	           	    expected: 527
        	           	actual  : 528
      	Test:       	TestOutputSizeP2SH

Expected Outcome We should add some tolerances so the test does not fail anymore.