`_hmac`: GIL may be released while attempting to set an exception

[picnixz]

Bug report

Bug description:

When calling hmac.update(), if the HACL* call fails, an exception is set. But this happens while we're releasing the GIL, which is not good.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other, Linux

Linked PRs

• gh-135561: ensure that the GIL is held when handling an HACL* error in _hmac #135562