pin toolchain for rustdoc-v26

[fprasx]

No description provided.

[fprasx]

This log line from rustup indicates that the action is not correctly overriding the toolchain file (this was from attempting to use 1.72:

info: note that the toolchain '1.73-x86_64-unknown-linux-gnu' is currently in use 
(overridden by '.../rust-toolchain.toml')

which indicates that the action is not correctly overriding the toolchain file. rustup override set $TOOLCHAIN seems to work locally. Issue: actions-rust-lang/setup-rust-toolchain#31

Confusingly though, the test cases are still failing. This seems related to ./scripts/regenerate_test_rustdocs.sh being explicitly invoked with +$TOOLCHAIN, while cargo is not. Explicitly invoking cargo with +$TOOLCHAIN fixes things. I'm not sure why the adapter compiled and run under 1.73 would be incompatible with rustdoc generated by 1.72.

It seems like we can wait for the action to merge a fix or merge this PR as is. Once we decide a course of action I'll pin the toolchain for rustdoc-v27.

[obi1kenobi]

Let's merge this as-is. Since this is a branch that isn't the latest, I think it's probably not worth spending too much more energy on it.

Thanks for digging into the cause and opening the issue upstream, it looks good to me.

[fprasx]

Hype. PR for rustdoc-v27 coming up.