Update Makefile to generate neo.owl.gz

[balhoff]

Add gzipped OWL output.

This PR is only for testing a GitHub build at the moment.

[balhoff]

https://github.com/geneontology/neo/actions/runs/22194747127/job/64191996470 "succeeded in 8m 52s"

[balhoff]

Noting size of .ofn.gz for release purposes:

 ls -lh neo.o*
-rw-r--r--  1 jim  staff   1.7G Feb 19 14:03 neo.ofn
-rw-r--r--  1 jim  staff   2.1G Feb 19 13:58 neo.owl
-rw-r--r--  1 jim  staff   109M Feb 19 14:03 neo.ofn.gz

[balhoff]

I found that neo.owl and neo.ttl both gzip down to 63M, so they compress even better. We can stick with .owl for old times' sake.