Adjust CI to how the ui test suite works

.github/driver.sh

@@ -27,9 +27,9 @@ test "$sysroot" = $desired_sysroot
 # Make sure this isn't set - clippy-driver should cope without it
 unset CARGO_MANIFEST_DIR
 
-# Run a lint and make sure it produces the expected output. It's also expected to exit with code 1
+# Run a lint and make sure it produces the expected output. It's also expected to exit with code 0
 # FIXME: How to match the clippy invocation in compile-test.rs?
-./target/debug/clippy-driver -Dwarnings -Aunused -Zui-testing --emit metadata --crate-type bin tests/ui/double_neg.rs 2>double_neg.stderr && exit 1
+./target/debug/clippy-driver -Aunused -Zui-testing --emit metadata --crate-type bin tests/ui/double_neg.rs 2>double_neg.stderr || exit 1
 sed -e "s,tests/ui,\$DIR," -e "/= help/d" double_neg.stderr >normalized.stderr
 diff -u normalized.stderr tests/ui/double_neg.stderr