[3.14] gh-145028: Fix blake2 tests in test_hashlib when it is missing due to configure --without-builtin-hashlib-hashes (GH-145029) (#145164)

[3.14] gh-145028: Fix blake2 tests in test_hashlib when it is missing due to build config (GH-145029)

specifically configure --without-builtin-hashlib-hashes means the otherwise guaranteed available blake2 family will not exist.  this allows the test suite to still pass.
(cherry picked from commit 273d5062ca17ac47354486f3fc6e672a04cf22e0)