Limit percentage round-trip test to 100% maximum #403

Job	Run time
Linux (nightly, --features malloc_size_of)	2m 9s
Linux (stable, --features dummy_match_byte)	41s
Linux (stable)	31s
Linux (beta, --features malloc_size_of)	35s
Linux (beta)	34s
Linux (nightly)	2m 15s
Linux (nightly, --features dummy_match_byte)	2m 15s
Linux (1.68.0, --features dummy_match_byte)	1m 50s
Linux (1.68.0, --features malloc_size_of)	1m 50s
Linux (beta, --features dummy_match_byte)	32s
Linux (stable, --features malloc_size_of)	39s
Linux (1.68.0)	2m 25s
Linux (nightly, --features bench,dummy_match_byte)	5m 25s
Linux (nightly, --features bench)	5m 14s
Result	3s
	26m 58s

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