Auto merge of #76210 - Mark-Simulacrum:tracing-update, r=oli-obk

Auto merge of #76210 - Mark-Simulacrum:tracing-update, r=oli-obk

Tracing update

This does not bring the more significant changes that are coming down the pipeline, but since I've already prepared the PR leaving it up :)

See https://github.com/rust-lang/rust/pull/76210#issuecomment-685065938:
> Unfortunately, tracing 0.1.20 — which contained the change to reduce the amount of code generated by the tracing macros — had to be yanked, as it broke previously-compiling code for some downstream crates. I've not yet had the chance to fix this and release a new patch. So, in order to benefit from the changes to reduce generated code, you'll need to wait until there's a new version of tracing as well as tracing-attributes and tracing-core.