Cannot set `write.data.path` to a subdirectory under the current table location OPTIMIZED_SIBLING_CHECK=true

### Describe the bug

Currently, when updating write.data.path of the table to a subdir under the table location, it will fail the location overlap check. This seems to be a regression since https://github.com/apache/polaris/pull/1686/changes#diff-1e0bdc1f194df7cceed5d4b2ddad483199b80d090a1c682f92ecf5fec5f83b2f

### To Reproduce

For example
```
spark-sql> ALTER TABLE tb1 SET TBLPROPERTIES (
'write.data.path' = '/alternative_data'
);

org.apache.iceberg.exceptions.ForbiddenException: Forbidden: Unable to create table at location 's3://' because it conflicts with existing table or namespace at location 's3://`
```

### Actual Behavior

_No response_

### Expected Behavior

The `validateNoLocationOverlap` should only prevent updating table location to be the same or child of sibling table's locations, not itself. Setting `write.data.path` to `/alternative` instead of the default `/data` should be a valid use case

### Additional context

The issue exists in both the active `validateNoLocationOverlap` path and the `OPTIMIZED_SIBLING_CHECK` path. The later have some other issues as described here: https://github.com/apache/polaris/issues/3378

### System information

_No response_

Trace the validateNoLocationOverlap path and the OPTIMIZED_SIBLING_CHECK path described in the issue, then compare them with the regression discussed in pull request 1686 and the related concerns in issue 3378. Reproduce the ALTER TABLE example and verify that changing write.data.path to a child directory of the same table location succeeds while sibling-table overlaps remain rejected.

Written by the indexing model from the issue text.