fix mldsa test case for buffer size and expire date

[JacobBarthelmeh]

Size of certificate being signed could be larger than the test buffer. Steps to hit the failing test case is:

./configure --enable-kyber --enable-dilithium --enable-all CC="clang -g -fsanitize=address"
make
for i in {1..10000}; do echo "Test $i"; ./tests/unit.test -372 -373 &> stdout.txt; if [ "$?" != "0" ]; then echo "Caught a failure"; break; fi done

[JacobBarthelmeh]

Retest this please Jenkins:

Found unhandled org.jenkinsci.plugins.workflow.support.steps.AgentOfflineException exception: