[Ocaml] Fix missing space on models

[Zomzog]

It's not covered by generated tests. Maybe I can add one?

fix #7738

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ping @cgensoul

[wing328]

It's not covered by generated tests. Maybe I can add one?

We can use https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml instead which covers a lot more edge cases but the OCaml client generator may not be ready to handle all these.