Revert "Show test issues as annotations in the GitHub Actions job summary"

This reverts commit 3a5ff35928.

Annotations were not actually appearing.
<https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/workflow-commands-for-github-actions>

test/run-tests.sh

@@ -63,7 +63,7 @@ test_downstream() { # owner repo make-target build-file build-hash
 	make -j4 "$3" RGBDS=../../
 	hash="$(sha1sum -b "$4" | head -c 40)"
 	if [ "$hash" != "$5" ]; then
-		echo >&2 '::warning SHA-1 hash of '"$4"' did not match: '"$hash"
+		echo >&2 'SHA-1 hash of '"$4"' did not match: '"$hash"
 		return 1
 	fi
 	popd