Print a GitHub Actions error annotation if install_deps.sh fails

See https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-commands#setting-an-error-message

.github/scripts/install_deps.sh

@@ -3,7 +3,7 @@
 set -eu
 
 case "${1%-*}" in
-	ubuntu)
+	ubuntu|debian)
 		sudo apt-get -qq update
 		sudo apt-get install -yq bison libpng-dev pkg-config
 		;;
@@ -27,7 +27,7 @@ case "${1%-*}" in
 		bison() { win_bison "$@"; } # An alias doesn't work, so we use a function instead.
 		;;
 	*)
-		echo "WARNING: Cannot install deps for OS '$1'"
+		echo "::error:: Cannot install deps for OS '$1'"
 		;;
 esac