fix: replace hardcoded unit number with newunit in test_diag_integral… #54

Job	Run time
build (--disable-openmp, --with-yaml)	10m 48s
build (--disable-openmp, --enable-test-input=/home/unit_tests_input)	10m 48s
build (--disable-setting-flags, --with-yaml)	10m 48s
build (--disable-setting-flags, --enable-test-input=/home/unit_tests_input)	10m 14s
build (--with-mpi=no, --with-yaml)	4m 14s
build (--disable-r8-default, --with-yaml)	10m 48s
build (--disable-r8-default, --enable-test-input=/home/unit_tests_input)	10m 41s
	1h 8m 21s

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