Remove hardcoded build patch from test script

[iyanmv]

If a user has passed a custom build path to cmake, and then calls for example ninja -C <custom_build_path> run_tests, the script test_acvp_vectors.py fails due to having "build" harcoded in the calls.

Instead, let's use helpers.get_current_build_dir_name() to get the build path and use that instead. This is already done in other scripts (e.g., test_binary.py)

Fixes #1937

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider will also need to be ready for review and merge by the time this is merged.)

[dstebila]

Thanks for the fix!

We're about to make a release of liboqs 0.11.0 from the main branch, so let's hold off on merging this until then.

[SWilson4]

LGTM as well, but since my approval will enable merge I will hold off on approving until after the release. Thanks very much for the contribution, @iyanmv.