link to PDF documentation broken for 1.8.0

[matthias314]

The link to the PDF documentation on the Julia 1.8 Documentation page results in "404: Not Found".

[mortenpi]

The PDF build for 1.8 needs #45290 and so didn't deploy automatically. I pushed a manual build instead and it's available now: https://raw.githubusercontent.com/JuliaLang/docs.julialang.org/assets/julia-1.8.0.pdf