Change l to n for loop index #12

Job	Run time
build-openmp	2m 41s
build-symmetric	2m 47s
build-repro	3m 3s
build-asymmetric	2m 45s
build-target	0s
test-layout	1m 35s
test-grid	1m 51s
test-restart	1m 41s
test-rotate	1m 39s
test-nan	1m 40s
test-dim (t, time)	1m 51s
test-dim (h, vertical thickness)	2m 48s
test-openmp	2m 1s
test-dim (l, horizontal length)	1m 51s
test-dim (r, density)	2m 17s
test-dim (q, enthalpy)	1m 49s
test-dim (z, vertical coordinate)	2m 34s
test-regression	0s
test-repro	1m 25s
cleanup-push	5s
cleanup-common	6s
cleanup-pr	0s
	36m 29s

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