Add missing include paths for `pineappl_applgrid` #74

Job	Run time
cli-macos (macos-latest, x86_64-apple-darwin)	3m 55s
cli-linux (x86_64-unknown-linux-gnu)	3m 31s
cli-macos (macos-14, aarch64-apple-darwin)	3m 38s
capi-macos (x86_64-apple-darwin)	13m 17s
capi-linux (x86_64-unknown-linux-gnu)	2m 12s
capi-macos (aarch64-apple-darwin)	15m 4s
create-release	0s
publish-crates	0s
wheels-eol-linux (x86_64)	1m 31s
wheels-linux (x86_64)	4m 57s
wheels-sdist	15s
wheels-macos (aarch64)	6m 41s
wheels-windows (x64)	7m 24s
wheels-macos (x86_64)	6m 26s
Release	0s
publish-release	0s
	1h 8m 51s

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