FILTER_GROUP: Tweak default group for nightly job

The groups are only include the GNU combinations now for CI on tf.org.

Nightly (228 configs):
    nightly_test_gnu
    nightly_profile_gnu
    nightly_psa_api_gnu
    nightly_ff_gnu
    nightly_otp_gnu

Change-Id: Ica02973f0aad3b971f6ad72a72438f5982717508
Signed-off-by: Karl Zhang <karl.zhang@arm.com>
1 file changed