Correct limit for test on target fields and remove duplicate assertions #4149

Job	Run time
copyright_headers	15s
cppcheck	7m 31s
black	48s
flake8	25s
forbidden_types	11s
lychee_IGNORED	19s
clang-format	20s
mypy	38s
pydocstyle	18s
pylint	48s
rstcheck	26s
unused_names	13s
vale	35s
sphinx-rtd	4m 33s
sphinx-conda	0s
build_macos (macos-latest, clang, openmp, mpi, python, gsl, ltdl, boost, hdf5, optimize, warning)	27m 39s
build_linux (ubuntu-20.04, gcc, boost, optimize, warning)	15m 4s
build_linux (ubuntu-20.04, gcc, openmp, python, gsl, ltdl, boost, optimize, warning)	22m 52s
build_linux (ubuntu-20.04, gcc, mpi, python, gsl, ltdl, boost, optimize, warning)	19m 43s
build_linux (ubuntu-20.04, gcc, openmp, mpi, python, gsl, ltdl, boost, hdf5, sionlib, libneurosim...	31m 33s
	2h 14m 11s

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