[#1285] Test the administration connector after MSI upgrade (#1286)

The Windows MSI upgrade test checks LDAPS after upgrading from 5.1.2,
but does not check the administration connector. Run `dsconfig
list-backends` over port 4444 after the upgraded service starts and fail
the job if the command fails.

Validation: `actionlint`, YAML parsing, and `git diff --check` passed.
The Windows MSI job has not been run locally.

Related to #1285.