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

.github/workflows/tests.yml

@@ -85,6 +85,7 @@ jobs:
         uses: dtolnay/rust-toolchain@e97e2d8cc328f1b50210efc529dca0028893a2d9
         with:
           toolchain: stable
+          components: clippy
 
       - name: Setup compilation cache
         uses: Swatinem/rust-cache@98c8021b550208e191a6a3145459bfc9fb29c4c0 # v2.8.0

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}");
 }