MueLu: potential aggregation bug

[jhux2]

Classic aggregation may not be handling Dirichlet BCs correctly.

Permalink to the relevant code on the develop branch:
https://github.com/jhux2/Trilinos/blob/develop/packages/muelu/src/Graph/UncoupledAggregation/MueLu_AggregationPhase1Algorithm_def.hpp#L80-L100

[github-actions]

Automatic mention of the @trilinos/muelu team