[PWGEM] forced dalitz decay: fix missing width (#2280)

- Fix missing dimond width[2] setting

Author: mhemmer-cern

MC/config/PWGEM/ini/pythia8_pp_13600_ForcedDalitz.ini

@@ -1,3 +1,6 @@
+[Diamond]
+width[2]=6.0
+
 [GeneratorPythia8]
 config=${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGEM/pythia8/generator/configPythia_ForcedDalitz.cfg