fix(snippet): should emit only one diagnostic

[Sec-ant]

Summary

A snippet must emit only ONE diagnostic.

biome/crates/biome_analyze/CONTRIBUTING.md

Line 183 in 8f9c14a

- When adding _invalid_ snippets in the `### Invalid` section, you must use the `expect_diagnostic` code block property. We use this property to generate a diagnostic and attach it to the snippet. A snippet **must emit only ONE diagnostic**.

Test Plan

[codspeed-hq]

CodSpeed Performance Report

Merging #2650 will not alter performance

_{Comparing fix/lint-doc-snippet (e8ab31e) with main (8f9c14a)}

Summary

✅ 90 untouched benchmarks