Exclude CTS attestation tests on GSI

For RKP to return attestations, the `remote_provisioning.hostname`
property needs to be set to the proper hostname to query for attestation
certs.

GSI doesn't set this property, so these tests fail on RKP-only devices.

Bug: 410503137
Test: Treehugger
Flag: TEST_ONLY
Change-Id: Ie6a0cbf5d72c383a6763c77906ddab38ff1831ec