2 PDF bugs : LHAPDF IDs changed between 6.5.3 and 6.5.4 / overlapping IDs

[agrohsje]

1.) LHAPDF IDs changed, see this PR for more details:
https://gitlab.com/hepcedar/lhapdf/-/commit/8cabf95d137ff4a1e05feae0ef1c66d19dca12eb

This means we need to adjust the PDF numbers when samples will be produced with LHAPDF >= 6.5.4

2.) There is another bug. For 4FS samples we have a problem in Powheg MSHT IDs are overlapping (hence the bug fix above)
MSHT20nnlo_nf4 has 65 members ; this conflicts with the id's of nf3 and nf4, so the code will crash:
27810 MSHT20nnlo_nf4 1
27860 MSHT20nnlo_as_smallrange_nf3 1
27870 MSHT20nnlo_as_smallrange_nf4 1 ?

@bbilin @lviliani @covarell @sihyunjeon @Cvico @DickyChant FYI