op-acceptance-tests: de-flakify `ecotone/TestFees`

[joshklop]

Consistently fails with:

    assertions.go:369:             ERROR[10-29|15:32:01.265] "\n\tError Trace:\t/Users/josh/repos/optimism/op-devstack/dsl/ecotone_fees.go:153\n\t            \t\t\t\t/Users/josh/repos/optimism/op-devstack/dsl/ecotone_fees.go:85\n\t            \t\t\t\t/Users/josh/repos/optimism/op-acceptance-tests/tests/ecotone/fees_test.go:27\n\tError:      \tNot equal: \n\t            \texpected: 31234414533497\n\t            \tactual  : 31233784533097\n\t            \t\n\t            \tDiff:\n\t            \t--- Expected\n\t            \t+++ Actual\n\t            \t@@ -3,3 +3,3 @@\n\t            \t  abs: (big.nat) (len=1) {\n\t            \t-  (big.Word) 31234414533497\n\t            \t+  (big.Word) 31233784533097\n\t            \t  }\n\tTest:       \tTestFees\n\tMessages:   \tWallet balance difference must equal total fees\n"