idl: bump the minor datamodel version for the 9.0 release (#6887)

This allows to reserve some minor versions for updates in the 8.x
release.

I've bumped it to 900 because 800 will make thing difficult if there are
more than 7 API changes in case of emergency.

Also related: there have been no "releases" made recently, does the
api_version_minor need to be bumped as well? (in
ocaml/idl/api_version.ml)

Author: lindig

ocaml/idl/datamodel_common.ml

@@ -10,7 +10,7 @@ open Datamodel_roles
               to leave a gap for potential hotfixes needing to increment the schema version.*)
 let schema_major_vsn = 5
 
-let schema_minor_vsn = 793
+let schema_minor_vsn = 900
 
 (* Historical schema versions just in case this is useful later *)
 let rio_schema_major_vsn = 5