8sp spacing for shimano differs from 7sp.
that’s why the usual trick to “upgrade” 7speed stuff is to take a 9sp cassette, bin 1 sprocket, and run it 8sp with 9sp shifters+mech.
No it really doesn’t.
7 and 8 speed have the same spacing, just the 7 speed cassette is 1 cog& spacer narrower.
9 speed cassettes (and 10 for that matter) are the same width as 8 but with narrower spacing.
So TL:DR 8 speed shifters will work fine on a 7 speed cassette, you’ll just have an unused click .