Fixed an include guard in `graph/instance.hpp` which was enabling an … #713

Job	Run time
build (ubuntu-24.04, 12.6.0, 13, bash, Unix Makefiles)	24s
build (ubuntu-24.04, 12.5.1, 13, bash, Unix Makefiles)	25s
build (ubuntu-20.04, 12.6.0, 10, bash, Unix Makefiles)	33s
build (ubuntu-20.04, 12.5.1, 10, bash, Unix Makefiles)	34s
build (ubuntu-20.04, 12.4.1, 10, bash, Unix Makefiles)	34s
build (ubuntu-20.04, 12.3.1, 10, bash, Unix Makefiles)	1m 27s
build (ubuntu-20.04, 12.2.2, 10, bash, Unix Makefiles)	1m 30s
build (ubuntu-20.04, 12.1.1, 10, bash, Unix Makefiles)	1m 23s
build (ubuntu-20.04, 12.0.1, 10, bash, Unix Makefiles)	1m 27s
build (ubuntu-20.04, 11.8, 10, bash, Unix Makefiles)	1m 24s
build (ubuntu-20.04, 11.7, 10, bash, Unix Makefiles)	1m 23s
build (ubuntu-20.04, 11.6.2, 10, bash, Unix Makefiles)	1m 20s
build (ubuntu-20.04, 11.6.1, 10, bash, Unix Makefiles)	1m 20s
build (ubuntu-20.04, 11.6, 10, bash, Unix Makefiles)	1m 20s
build (ubuntu-20.04, 11.5, 10, bash, Unix Makefiles)	1m 20s
build (ubuntu-20.04, 11.4, 10, bash, Unix Makefiles)	1m 17s
build (ubuntu-20.04, 11.3, 9, bash, Unix Makefiles)	51s
build (ubuntu-20.04, 11.2, 9, bash, Unix Makefiles)	37s
build (ubuntu-20.04, 11.1, 9, bash, Unix Makefiles)	29s
build (ubuntu-20.04, 11.0, 9, bash, Unix Makefiles)	27s
	20m 5s

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