chore: view subquery test case

[tianzhou]

Test case validate #104

[Copilot]

Pull Request Overview

This PR adds a test case to validate the handling of UNION and UNION ALL operators within view subqueries, addressing issue #104 in the pgschema repository.

Key changes:

• Added a new view union_subquery_view that tests UNION and UNION ALL in subqueries
• Updated test expectations to reflect 5 views instead of 4

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/diff/create_view/add_view/plan.txt	Updated plan output to include the new union_subquery_view in summary and DDL sections
testdata/diff/create_view/add_view/plan.sql	Added DDL for creating union_subquery_view with UNION and UNION ALL operators
testdata/diff/create_view/add_view/plan.json	Added JSON entry for the union_subquery_view creation operation
testdata/diff/create_view/add_view/new.sql	Added the source SQL definition for union_subquery_view with comprehensive comments
testdata/diff/create_view/add_view/diff.sql	Added the DDL diff showing the addition of union_subquery_view

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