Fix of FilterHit_tf.py to also propagate the HGTD hits

Fixes issue identified in ATLMCPROD-9129 (see this comment), where HGTD hits are not propagated in HITS merging step.

I've validated that this simple fix does indeed produce HGTD hits in the output file from FilterHit_tf.py using the s3656 tag without any modifications:

lxplus780:/afs/cern.ch/work/c/cohm/public/HGTD/21.9/s3656_merging > cat merge.sh
FilterHit_tf.py \
--AMI s3656 \
--runNumber 800360 \
--inputHITSFile ../../s3654_minbias_j*/800380*HITS.pool.root \
--outputHITS_FILTFile 800380.merged.HITS.pool.root 2>&1 | tee merge.log
lxplus780:/afs/cern.ch/work/c/cohm/public/HGTD/21.9/s3656_merging > checkFile.py 800380.merged.HITS.pool.root | grep HGTD
     319.862 kb      218.093 kb       13.631 kb        0.000       16  (B) SiHitCollection_p4_HGTD_Hits

Thanks @nstyles for the hint of the issue! Tagging @tadej, @dshope, @aleopold, @tawang, @lshan for info.

Best, Christian