CairoMakie ignores vspan alpha

[aplavin]

Running vspan(0..1, color=:red, alpha=0.1) results in this with GLMakie (expected):

and this with CairoMakie (alpha is ignored):

• what version of Makie are you running? (]st -m Makie) latest
• can you reproduce the bug with a fresh environment ? (]activate --temp; add Makie) latest
• What platform + GPU are you on? macbook m2

[lanceXwq]

I have the same problem. vspan(0..1, color=(:red, 0.1)) works while vspan(0..1, color=:red, alpha=0.1) does not. This also seems to happen to scatterlines.

[ffreyer]

This is more or less a duplicate of #3735, because vspan/hspan rely on poly. Whatever comes out of #4360 will most likely revamp the color internals so it's not a priority right now and it may get fixed there.