Add more variants of GPT2

[sgligorijevicTT]

Ticket

N/A

Problem description

We need more tests

What's changed

I refactored the folder structure of GPT2 tests and added more variants of the model

Checklist

• New/Existing tests provide coverage for changes

[github-actions]

	Tests	Passed ✅	Skipped ⚠️	Failed
TT-XLA Tests	455 ran	383 passed	72 skipped	0 failed

Test	Result
No test annotations available

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.03%. Comparing base (c1cb43a) to head (6b82a47).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #216   +/-   ##
=======================================
  Coverage   77.03%   77.03%           
=======================================
  Files          21       21           
  Lines        1006     1006           
=======================================
  Hits          775      775           
  Misses        231      231           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.