Renable test_add_indexes from test_index.py

[genedan]

I have disabled the unit test, test_add_indexes from faslr/tests/index/test_index.py. This test currently relies on dummy index data embedded within the modules that define the classes we are testing. This dummy data will be deleted and moved to the sample db, so we'll have to rewrite this test afterwards, until then it will fail.

[aminemanai2003]

I'd like to take this issue. I'll restore test_add_indexes using the sample database-backed index inventory (rather than deleted module-level dummy data), exercise the dialog selection through pytest-qt, and assert that the selected premium index is attached to the expected-loss model. I'll run the focused index tests and the broader suite where the local Qt environment permits.