[clang-tools-extra] Added missing comma

[zacharyselk]

Summary

The new diagnostic tool (D85545) caught a missing comma, adding one to fix the warning.

[kamaub]

This LGTM

clang-tools-extra/clangd/unittests/SemanticHighlightingTests.cpp

)cpp",
         operator $Class[[Foo]]();
       };
       void $Function[[f]]() {
         $Class[[Bar]] $LocalVariable[[B]];
         $Class[[Foo]] $LocalVariable[[F]] = $LocalVariable[[B]];
         $Class[[Foo]] *$LocalVariable[[FP]] = ($Class[[Foo]]*)$LocalVariable[[B]];
         int $LocalVariable[[I]] = (int)$LocalVariable[[B]];
       }
-    )cpp"
+    )cpp",
       R"cpp(
       struct $Class[[B]] {};
       struct $Class[[A]] {
         $Class[[B]] $Field[[BB]];
         $Class[[A]] &operator=($Class[[A]] &&$Parameter[[O]]);
       };
 
       $Class[[A]] &$Class[[A]]::operator=($Class[[A]] &&$Parameter[[O]]) = default;