Auto merge of #53433 - kennytm:rollup, r=kennytm

Auto merge of #53433 - kennytm:rollup, r=kennytm

Rollup of 10 pull requests

Successful merges:

 - #52946 (Documented impl From on line 367 of libserialize/json.rs)
 - #53234 (Remove Travis shutdown debug scripts, and remove CI-specific DNS settings)
 - #53313 (Two small improvements)
 - #53360 (Addressed #51602)
 - #53364 (Warn if the user tries to use GATs)
 - #53373 (Tweak unclosed delimiter parser error)
 - #53377 (std: Use target_pointer_width for BACKTRACE_ELF_SIZE)
 - #53395 (Use #[non_exhaustive] on internal enums)
 - #53399 (Tidy: ignore non-Markdown files when linting for the Unstable Book)
 - #53412 (syntax_ext: remove leftover span_err_if_not_stage0 macro.)