Fixing an ommitted conditional on a StrongBox test

testGenerate_EC_ModernSpec_AsCustomAsPossibleStrongbox was not being run
conditionally depending on if StrongBox was actually present on system.
This was causing it to fail incorrectly on device's that don't have a
StrongBox Secure Element

Test: atest
cts/tests/tests/keystore/src/android/keystore/cts/KeyPairGeneratorTest.java

Change-Id: I1a9bc9cbb92cf0e8a8b0c8519e2dad4868cf2a90