tests: Use BOOST_CHECK_EQUAL for verbose prints on fail #15942

This should print something like:

test/crypto_tests.cpp(557): error: in "crypto_tests/sha256d64": check str1 == str2 has failed [b185c0ca629130a6f4fbca4d0ac1164dcebb8e97eff941b1c03cdb406f66d70e != b185c0ca629130a6f4fbca4d0ac1164dcebb8e97eff941b1c03cdb406f66d70a]

In my experience, the specfic end-result hash values are quite useless when debugging bugs in SHA256 implementations, just too much mixing of bits

But not a strong NACK

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--174a7506f384e20aa4161008e828411d-->

Conflicts

Reviewers, this pull request conflicts with the following ones:

• #15649 (Add ChaCha20Poly1305@Bitcoin AEAD by jonasschnelli)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.