style: fix broken rustdoc comment (#9329)

* ci: lint for broken inline code / backticks

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

This breaks the rustdoc rendering.

* chore: apply rustdoc lint to workspace

Lint the entire workspace by specifying it in Cargo.toml.

Author: domodwyer

Cargo.toml

@@ -19,6 +19,9 @@ rust_2018_compatibility = "warn"
 rust_2021_compatibility = "warn"
 unused = "warn"
 
+[workspace.lints.rustdoc]
+unescaped_backticks = "warn"
+
 [workspace.lints.clippy]
 dbg_macro = "warn"
 todo = "warn"

src/tests/util/test_app.rs

@@ -116,7 +116,7 @@ impl TestApp {
     }
 
     /// Create a new user with a verified email address in the database
-    /// (`<username>@example.com``) and return a mock user session.
+    /// (`<username>@example.com`) and return a mock user session.
     ///
     /// This method updates the database directly
     pub fn db_new_user(&self, username: &str) -> MockCookieUser {