[umf] use alloc sizes that are multiples of 8 in tests #1958

Job	Run time
Build - MacOS (macos-12)	7m 16s
Build - MacOS (macos-13)	5m 28s
Build - Ubuntu (ubuntu-20.04, Debug, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENABLE...	9m 34s
Build - Ubuntu (ubuntu-20.04, Debug, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENABLE...	9m 55s
Build - Ubuntu (ubuntu-20.04, Release, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENAB...	12m 14s
Build - Ubuntu (ubuntu-20.04, Release, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENAB...	13m 43s
Build - Ubuntu (ubuntu-22.04, Debug, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENABLE...	9m 54s
Build - Ubuntu (ubuntu-22.04, Debug, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENABLE...	9m 31s
Build - Ubuntu (ubuntu-22.04, Release, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENAB...	10m 52s
Build - Ubuntu (ubuntu-22.04, Release, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF, -DUMF_ENAB...	12m 12s
Build - Ubuntu (ubuntu-22.04, Release, clang, clang++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=OFF)	15m 42s
Build - Ubuntu (ubuntu-22.04, Release, gcc, g++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=ON)	14m 18s
Build - Ubuntu (ubuntu-22.04, Release, clang, clang++, -DVAL_USE_LIBBACKTRACE_BACKTRACE=ON)	10m 59s
Build - Ubuntu (ubuntu-20.04, Release, gcc-7, g++-7)	10m 33s
Build - Windows (windows-2019, Debug)	8m 41s
Build - Windows (windows-2019, Release)	11m 35s
Build - Windows (windows-2022, Debug)	10m 14s
Build - Windows (windows-2022, Release)	14m 5s
	3h 16m 46s

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