Test main should use assert_frame_equal, not equals

Using equals does nothing, so the tests are actually failing.
We will have to re-run all the validation frames.
I just tried one, and running the same code in test_main as in development.py creates very different data exports. There must be some issue with the version - I don't understand yet. Probably related to #234

For example, test_growbikenet_case_success_offline_import_data3:

Output from development, using exact same code and import data: 321 rows

Output from test_growbikenet_case_success_offline_import_data3: 408 rows

Start in test_main at test_growbikenet_case_success_offline_import_data3 and compare its validation with the corresponding code in development.py. Replace the ineffective equality check with the requested frame comparison, then re-run the validation frames and investigate why the test produces 408 rows instead of 321. Done means the comparison detects mismatches and the export discrepancy is understood.

Written by the indexing model from the issue text.