rustdoc: source code viewer sometimes has extra scroll bar

[kadiwa4]

Notice the vertical scroll bar (on the right) where there isnt supposed to be one and the unaligned line numbers (because I scrolled):

The issue is easier to replicate for long source files.

Rust version: 1.59.0 and upwards

Replicating

macOS 13.1 / Safari 16.2

Open https://doc.rust-lang.org/1.66.0/src/core/num/uint_macros.rs.html; make sure the sidebar is expanded. Reload until you see the problematic scroll bar.

@rustbot label: +A-rustdoc-ui +C-bug +T-rustdoc