style: fix broken rustdoc comment

[domodwyer]

Cleans up the bad comment formatting I introduced in #9322, and enables a rustdoc lint to try and catch repeats in the future.

---

• ci: lint for broken inline code / backticks (559b51b)

  Enables the rustdoc "unescaped_backticks" lint[1] at warn level.
  
  Unfortunately this only covers "prod" code, so it doesn't catch the
  actual broken backticks in the test code!
  
  [1]: https://doc.rust-lang.org/rustdoc/lints.html#unescaped_backticks
  

• style: remove spurious backtick (5c34d66)

  This breaks the rustdoc rendering.
  

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.17%. Comparing base (c847b96) to head (a3cf0a6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9329   +/-   ##
=======================================
  Coverage   89.17%   89.17%           
=======================================
  Files         282      282           
  Lines       28913    28913           
=======================================
  Hits        25782    25782           
  Misses       3131     3131           

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