Add test to ensure the result descripton is correctly handling codeblocks

Author: GuillaumeGomez

src/test/rustdoc-gui/search-result-description.goml

@@ -0,0 +1,5 @@
+// This test is to ensure that the codeblocks are correctly rendered in the search results.
+goto: file://|DOC_PATH|/test_docs/index.html?search=some_more_function
+// Waiting for the search results to appear...
+wait-for: "#titles"
+assert: (".search-results .desc code", "format!")