ci: update pull request workflow (#67)

`actions/checkout@v3` is deprecated in favor of the next version.

Author: ps-kwang

.github/workflows/pull-request.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Deno
         uses: denoland/setup-deno@v1