column_diagnostics test: Fix syntax error in `Makefile.am` #921

Job	Run time
build (--disable-openmp, --with-yaml)	14m 31s
build (--disable-openmp, --enable-test-input=/home/unit_tests_input)	10m 24s
build (--disable-setting-flags, --with-yaml)	14m 23s
build (--disable-setting-flags, --enable-test-input=/home/unit_tests_input)	11m 20s
build (--with-mpi=no, --with-yaml)	4m 8s
build (--disable-r8-default, --with-yaml)	14m 40s
build (--disable-r8-default, --enable-test-input=/home/unit_tests_input)	10m 45s
	1h 20m 11s

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