Summary:
Renamed the cascade variable to yb_cascade in ATPrepSetTableSpace, as it is a YugabyteDB-specific parameter introduced in commit 06baaf0297e12ab950e41769ab2425fe82f0ae18 / D37055.

Jira: DB-12239

Test Plan: ./yb_build.sh --java-test org.yb.pgsql.TestPgRegressColocatedTablesWithTablespaces#testPgRegressColocatedTablesWithTablespaces

Reviewers: jason

Reviewed By: jason

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D38170