Test with error message descontruction

src/index.ts

@@ -27,14 +27,16 @@ const loadSecretsAction = async () => {
 		// Load secrets
 		await loadSecrets(shouldExportEnv);
 	} catch (error) {
-		// It's possible for the Error constructor to be modified to be anything
-		// in JavaScript, so the following code accounts for this possibility.
-		// https://kentcdodds.com/blog/get-a-catch-block-error-message-with-typescript
 		let message = "Unknown Error";
 		if (error instanceof Error) {
 			message = error.message;
-		} else {
+			if (message === "Unknown Error" && error.cause instanceof Error) {
-			message = String(error);
+				message = error.cause.message;
+			}
+		} else if (error && typeof error === "object" && "message" in error && typeof (error as { message: unknown }).message === "string") {
+			message = (error as { message: string }).message;
+		} else if (error !== null && error !== undefined) {
+			message = typeof error === "string" ? error : JSON.stringify(error);
 		}
 		core.setFailed(message);
 	}