`PSA_ALG_AEAD_WITH_SHORTENED_TAG(aead_alg, len) == aead_alg` when
`len == PSA_AEAD_TAG_LENGTH(aead_alg)`. So skip this case when testing
the printing of constants.
This fixes one test case due to the way arguments of
`PSA_ALG_AEAD_WITH_SHORTENED_TAG` are enumerated (all algorithms are tested
for a value of `len` which isn't problematic, and all values of `len` are
tested for one algorithm).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>