Update CI workflow to install Bun directly via script

- Replaced the Bun setup action with a script to install Bun and update the PATH.
- Ensured Bun's binary directory is added to the GitHub environment for subsequent steps.

.gitea/workflows/ci.yml

@@ -14,7 +14,10 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Setup Bun
-        uses: oven-sh/setup-bun@v2
+        run: |
+          curl -fsSL https://bun.sh/install | bash
+          echo "$HOME/.bun/bin" >> $GITHUB_PATH
+          echo "PATH=$HOME/.bun/bin:$PATH" >> $GITHUB_ENV
 
       - name: Install dependencies
         run: bun install