v3: Fix bad MPI_STACK behavior

This release of v3 fixes some bad behavior from calling the MPI_STACK detection multiple times (due to CMake caching).

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From CHANGELOG.md

Fixed

• Fixed bad behavior in the MPI_STACK detection on subsequent calls to DetermineMPIStack

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What's Changed

• v3: Fix multiple MPI_STACK sets by @mathomp4 in #415

Full Changelog: v3.54.0...v3.55.0