Do not hide test output in log file

Putting the clippy output in a log file is somewhat convenient for
local use. But if there's a failure in CI that's difficult to reproduce
locally, it only makes things harder to debug.

Author: senekor

rust-tooling/ci-tests/tests/stubs_are_warning_free.rs

@@ -73,12 +73,5 @@ fn stubs_are_warning_free() {
     if !log.is_empty() {
         std::fs::write("clippy.log", &log).expect("should write clippy.log");
     }
-    assert!(
-        log.is_empty(),
-        "
-    ╔═════════════════════════════════════════╗
-    ║ clippy found warnings, check clippy.log ║
-    ╚═════════════════════════════════════════╝
-    "
-    );
+    assert!(log.is_empty(), "{log}");
 }