[CI] Enable testing for regressions in the compare_to_enc tests

In merge request pipelines (to main), we currently run two sets of tests against ivas-float update, one with fx decoder, one with fx encoder. Only the fx decoder tests check for regressions in an MR. We omitted this for the encoder at first because we wanted to wait for it to be more stable. This should be enabled at some point.

Pros:

• detect regressions for encoder changes as well
• for e.g. bit-exact optimizations, it is very important to know if the bit-exactness actually holds

cons:

• encoder is not super stable, expecially stereo still needs work, might need to use [allow-regressions] tag a lot
• will slow down pipeline as codec needs to be run twice