Fix `APPL_IGRID_DIR` determination #72

Job	Run time
capi-linux (x86_64-unknown-linux-gnu)	4m 8s
cli-macos (macos-latest, x86_64-apple-darwin)	2m 47s
capi-macos (x86_64-apple-darwin)	11m 8s
cli-linux (x86_64-unknown-linux-gnu)	3m 36s
capi-macos (aarch64-apple-darwin)	7m 53s
create-release	0s
cli-macos (macos-14, aarch64-apple-darwin)	3m 5s
publish-crates	0s
wheels-eol-linux (x86_64)	1m 21s
wheels-macos (aarch64)	11m 7s
wheels-linux (x86_64)	4m 46s
wheels-sdist	12s
wheels-macos (x86_64)	7m 42s
wheels-windows (x64)	8m 17s
publish-release	0s
Release	0s
	1h 6m 2s

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