openapi-to-tsp test should be moved to a regression test job/improved

They are very slow, more than 50% of the whole test time spend in thie repo is that test. What they are doing is closer to what is happening the regression test.

Locate the openapi-to-tsp test and compare its runtime with the rest of the test suite; the issue reports that it consumes more than half of the repository's test time. Inspect how regression test jobs are organized and determine how this test can run there instead, with completion shown by faster regular tests and successful regression coverage.

Written by the indexing model from the issue text.