Adjust behaviour when unsupported species in junction standardisation

[yutanagano]

• In all other standardisation functions, if species unsupported then standardisation is skipped
• This is not the case in new junction standardisation, it raises ValueError
• This should be unified

[LonnekeScheffer]

In the V3 revision this does not raise a ValueError anymore (skip standardization and return Junction object with error inside), I think this issue can be closed?

[yutanagano]

Yes, good point. When we come to merge the V3 branch to main on release I will mark this to be closed by that PR.