PFRICH: restore sensititvity to hits (#715)

Fixes a minor regression from the latest geometry update in #664.

Fixes: #706

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/PFRICH_geo.cpp

@@ -305,6 +305,7 @@ static Ref_t createDetector(Detector& description, xml_h e, SensitiveDetector se
   Volume hrppdVol_air(detName + "_air_hrppd", hrppd_Solid, air);
   Volume hrppdVol(detName + "_hrppd", hrppd_Solid, sensorMat);
 
+  hrppdVol_air.setSensitiveDetector(sens);
   hrppdVol_air.setVisAttributes(gasvolVis);
   DetElement hrppdDE(sdet, "hrppd_de", 0);