Migrate the single `SubcommandEndToEndTestsXCTest` suite to Swift Testing

While addressing #710, there was a single test suite that was not converted as it used `XCTestExpectation`.

We need to understand the test intent before migration.

At the time of writing, #951 did not migrate that test suite and renamed it to `SubcommandEndToEndTestsXCTest`.

Locate the SubcommandEndToEndTestsXCTest suite and read its XCTestExpectation usage to understand the test intent. Review the context from #710 and the migration in #951, then run the relevant test target. Done means this remaining suite is migrated to Swift Testing without losing its end-to-end coverage.

Written by the indexing model from the issue text.