[regression-test](auth) Scope export cancel by label

[shuke987]

Summary

Fix auth_call/test_dml_export_table_auth by scoping CANCEL EXPORT to the case-local export label.

The case previously cancelled by WHERE STATE = "EXPORTING". In concurrent Cloud P0 runs this can match an unrelated export job from another suite, such as test_export_variant_10k, and then fail with an unrelated permission denied error.

This patch adds an explicit export label and uses WHERE LABEL = "${exportLabel}" for both cancel statements, preserving the auth test intent while avoiding cross-suite export job interference.

Testing

• git diff --check -- regression-test/suites/auth_call/test_dml_export_table_auth.groovy
• Not run locally: requires a configured Cloud/S3 regression environment

[shuke987]

run buildall

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