Fix CodeQL findings in oracle/apex/apexlang/tools/apexctl.mjs

This issue is similar to "Insecure temporary file, line 4342" from #103.

Insecure temporary file, line 96

The suggested fix could be as simple as

async function writeJson(filePath, payload) {
  await fs.writeFile(filePath, JSON.stringify(payload, null, 2) + "\n", { encoding: "utf8", mode: 0o600 });
}