fix array indices for horiz_interp_type assignment test #867

Job	Run time
build (-DOPENMP=on, -DCMAKE_BUILD_TYPE=Release)	11m 20s
build (-DOPENMP=on, -DCMAKE_BUILD_TYPE=Debug)	3m 32s
build (-DOPENMP=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Release)	12m 44s
build (-DOPENMP=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Debug)	3m 47s
build (-DOPENMP=on, -DWITH_YAML=on, -DCMAKE_BUILD_TYPE=Release)	12m 8s
build (-DOPENMP=on, -DWITH_YAML=on, -DCMAKE_BUILD_TYPE=Debug)	3m 39s
build (-DOPENMP=on, -DWITH_YAML=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Release)	13m 24s
build (-DOPENMP=on, -DWITH_YAML=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Debug)	4m 4s
build (-DOPENMP=off, -DCMAKE_BUILD_TYPE=Release)	11m 24s
build (-DOPENMP=off, -DCMAKE_BUILD_TYPE=Debug)	3m 32s
build (-DOPENMP=off, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Release)	12m 39s
build (-DOPENMP=off, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Debug)	3m 47s
build (-DOPENMP=off, -DWITH_YAML=on, -DCMAKE_BUILD_TYPE=Release)	12m 2s
build (-DOPENMP=off, -DWITH_YAML=on, -DCMAKE_BUILD_TYPE=Debug)	3m 57s
build (-DOPENMP=off, -DWITH_YAML=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Release)	12m 51s
build (-DOPENMP=off, -DWITH_YAML=on, -DUSE_DEPRECATED_IO=on, -DCMAKE_BUILD_TYPE=Debug)	4m 0s
	2h 8m 50s

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