Offline documentation incorrectly links primitives to online one

[MultisampledNight]

The front page of std, opened with rustup doc std, lists this paragraph:

Note the documentation for the primitives str and [T] (also called ‘slice’). Many method calls on String and Vec<T> are actually calls to methods on str and [T] respectively, via deref coercions.

While clicking the links of String and Vec<T> correctly lead to their offline sites as well, str and [T] link to https://doc.rust-lang.org/1.55.0/std/ instead, which isn't available without an internet connection!

I've observed this on stable (1.55.0), likely a regression of #79630.

@jyn514 @GuillaumeGomez

[jyn514]

Duplicate of #79630, #87073 hasn't hit stable yet.