(DO NOT MERGE) Don't call json::extract_rendered for non-compiler output

Author: Zalathar

Diff for: src/tools/compiletest/src/runtest.rs

@@ -3892,7 +3892,7 @@ impl<'test> TestCx<'test> {
 
         let stderr = if self.force_color_svg() {
             anstyle_svg::Term::new().render_svg(&proc_res.stderr)
-        } else if explicit_format {
+        } else if explicit_format || matches!(output_kind, TestOutput::Run) {
             proc_res.stderr.clone()
         } else {
             json::extract_rendered(&proc_res.stderr)