Bump third_party/imgui/repo from `2860d7b` to `030746f` #1664

Job	Run time
Build on Darwin (clang, simulated)	47m 51s
Build on Linux (fake, gcc_release, clang, simulated)	52m 17s
Build on Linux (coverage)	19m 48s
Build on Linux (gcc_debug)	52m 34s
Build on Linux (python_lib)	20m 1s
Build on Linux (python lighting-app)	5m 30s
	3h 18m 1s

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