CI: silence confusing --help output in workflows/test.sh (#1276)

This PR silences some confusing help text output during data installation by `g.download.location`:

For the error, see
https://github.com/neteler/grass-addons/actions/runs/12647834206/job/35240965201

Additionally: comment added.

.github/workflows/test.sh

@@ -4,10 +4,12 @@
 set -e
 
 # Install module from addons if not available (in v7).
-if ! grass --tmp-project XY --exec g.download.location --help; then
+if ! grass --tmp-project XY --exec g.download.location --help 2>1; then
     grass --tmp-project XY --exec \
         g.extension g.download.location
 fi
+
+# note: g.download.location is a wrapper around g.download.project
 grass --tmp-project XY --exec \
     g.download.location url=https://grass.osgeo.org/sampledata/north_carolina/nc_spm_full_v2alpha2.tar.gz path=$HOME