[WIP] fix multigrid agglomeration #8259

Job	Run time
Build SU2 (BaseMPI)	13m 45s
Build SU2 (asan) (BaseNoMPI-asan)	7m 20s
Build SU2 (tsan) (BaseOMP-tsan)	12m 32s
Build SU2 (ReverseMPI)	4m 44s
Build SU2 (asan) (ReverseNoMPI-asan)	9m 52s
Build SU2 (tsan) (ReverseOMP-tsan)	26m 51s
Build SU2 (ForwardMPI)	4m 16s
Build SU2 (BaseNoMPI)	3m 41s
Build SU2 (ReverseNoMPI)	4m 0s
Build SU2 (ForwardNoMPI)	3m 46s
Build SU2 (BaseOMP)	3m 22s
Build SU2 (ReverseOMP)	4m 45s
Build SU2 (ForwardOMP)	3m 28s
Address Sanitizer Tests	0s
Regression Tests	0s
Unit Tests	0s
Thread Sanitizer Tests (hybrid_regression.py)	27m 29s
Thread Sanitizer Tests (hybrid_regression_AD.py)	10m 50s
	2h 20m 41s

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