chore(build): remove corepack & fetch gitmodules on checkout (MisskeyIO#840)

.github/workflows/validate-api-json.yml

@@ -21,7 +21,7 @@ jobs:
         node-version: [22.x]
 
     steps:
-    - uses: actions/checkout@v4.1.1
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
         submodules: true
@@ -36,7 +36,6 @@ jobs:
         cache: 'pnpm'
     - name: Install Redocly CLI
       run: npm i -g @redocly/cli
-    - run: corepack enable
     - run: pnpm i --frozen-lockfile
     - name: Check pnpm-lock.yaml
       run: git diff --exit-code pnpm-lock.yaml