Understand and fix test-graphsync_identity_cid failure

[BigLep]

As part of the nv27 release process of upgrading to a new Lotus version (v1.34.x), test-graphsync_identity_cid started to fail. This was discussed and investigated in https://filecoinproject.slack.com/archives/CP50PPW2X/p1757062730456229 by @LexLuthr and @rvagg . We didn't come to understanding as to why the test was failing, and instead disabled it in https://github.com/filecoin-project/boost/pull/2018.

The test's failure does indicate the possibility of a more fundamental problem that we need to understand as it may have broader impact (including Curio). We think there’s just some specific combination of config or setup in this test that is exposing, and we're currently crossing our fingers that it isn't a critical retrieval bug that will affect SPs.