avoid ggHH_SMEFT multiple-insertion crash - replace with SMEFTtruncation

Oleksii Kurdyshrequested to merge
okurdysh/athena:Powheg_23.6.42Fix into main

in JO when using PowhegConfig.multiple-insertion = X got a crash of type "SyntaxError: cannot assign to expression here" which I guess because hyphens are illegal to use in variable names. But actually in current version of ggHH_SMEFT, according to .tex in /cvmfs/atlas.cern.ch/repo/sw/Generators/powheg/ATLASOTF-07-09-x86_64/POWHEG-BOX-V2/ggHH_SMEFT/Docs/ multiple-insertion is replaced by SMEFTtruncation. This luckily also doesn't have hyphen and fixes the problem and that's what MR is about.

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