Drop one more trailing comma flagged by clippy 1.95 on -next

The stdlib-manifest sentinel test (`manifest_includes_rust_standard_library`)
has the same `unnecessary_trailing_comma` pattern that the prior
commit cleaned up in the test-bench files. The test lives only on
-next (it asserts on the synthetic stdlib entry that -next adds in
`build.rs`), so the miss wasn't caught until the rebase brought
these files together under clippy 1.95.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: EliahKagan

src/licenses/embedded.rs

@@ -225,7 +225,7 @@ mod tests {
             Some("Apache-2.0 OR MIT"),
             "stdlib license should be Apache-2.0 OR MIT",
         );
-        assert!(!stdlib.files.is_empty(), "stdlib entry must have license text",);
+        assert!(!stdlib.files.is_empty(), "stdlib entry must have license text");
     }
 
     /// Workspace members with different license or authorship must appear