Ignore results from ops on `ref` benchmarks #201

Job	Run time
build-on-lower-bound (ubuntu-latest, 4.12.x)	1m 33s
build-windows (ocaml.5.2.1,ocaml-option-mingw)	3m 51s
build-windows (ocaml.5.3.0,ocaml-option-mingw)	3m 55s
	9m 19s

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