Backport to branch(3) : Add alter column type tests for imported tables

[feeblefakie]

This is an automated request for a manual backport of the following:

• Original PR: Add alter column type tests for imported tables #3058
• Commit to backport: 4a4d176

1. Resolve any conflicts that occur during the cherry-picking process.

git fetch origin &&
git checkout 3-pull-3058 &&
git cherry-pick --no-rerere-autoupdate -m1 4a4d17609803ecccb49383798ce1ed0f5dd8af26

2. Push the changes.
3. Merge this PR after all checks have passed.

Thank you!

[KodaiD]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds integration tests for altering column types on imported tables. The changes are mostly in test files and look good overall. I've identified several areas with code duplication across the new tests, particularly in the test setup (Arrange blocks) and the Act/Assert logic. I've provided suggestions to refactor this duplicated code into helper methods or by restructuring the test logic to improve maintainability and readability. Additionally, there's a minor simplification possible in one of the new utility methods.