fix(ci): use .mjs

Author: tutinoko2048

.github/workflows/manifest/action.yml

@@ -6,5 +6,5 @@ outputs:
     description: 'the name of the file.'
 
 runs:
-  using: 'node16'
-  main: 'index.js'
+  using: 'node20'
+  main: 'index.mjs'

.github/workflows/manifest/index.js renamed to .github/workflows/manifest/index.mjs

@@ -1,6 +1,6 @@
-const core = require('@actions/core');
-const github = require('@actions/github');
-const fs = require('fs');
+import * as core from '@actions/core';
+import * as github from '@actions/github';
+import * as fs from 'fs';
 
 try {
   const json = fs.readFileSync('manifest.json').toString();