docs(agents): fix link reference in docstring

Link reference defined in list item is not shown in rendered
docstring.

<https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#doc_nested_refdefs>

Caught by Clippy.

Author: jakewilliami

ua_generator/src/lib.rs

@@ -7,7 +7,7 @@
 //!
 //!
 //! - **Generate** get a random UA to use.
-//!   - [`spoof_ua`]: ua/fn.spoof_ua.html
+//!   - [`spoof_ua`][]: ua/fn.spoof_ua.html
 //!
 //! # Basic usage
 //!