Add opcode_size for nop so we don't get errors (#2060) #996

Job	Run time
install (dev, macOS, macos-latest, 4.14.2)	35m 26s
install (8.19.0, Ubuntu, ubuntu-latest, 4.09.1)	40m 37s
install (8.20.0, macOS, macos-latest, 4.14.2)	34m 38s
install (8.20.0, Ubuntu, ubuntu-latest, 4.09.1)	39m 21s
install (8.19.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 34m 58s
install (dev, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml/oc...	1h 33m 2s
install (8.19.0, macOS, macos-latest, 4.14.2)	37m 55s
install (8.18.0, Ubuntu, ubuntu-latest, 4.09.1)	42m 9s
install (8.20.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 35m 44s
install (dev, Ubuntu, ubuntu-latest, 4.09.1)	38m 21s
install (8.18.0, macOS, macos-latest, 4.14.2)	33m 41s
install (8.18.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 38m 14s
	11h 24m 6s

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