ci: run test on default image + install Bun (Node-less bun container broke checkout)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -27,13 +27,17 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  # ---- test: typecheck + unit tests, in the Bun image ----------------------
+  # ---- test: typecheck + unit tests ----------------------------------------
+  # Runs on the default runner image (has Node, which actions/checkout needs);
+  # Bun is installed in a step rather than via a Node-less bun container.
   test:
     runs-on: ubuntu-latest
-    container:
-      image: oven/bun:1
     steps:
       - uses: actions/checkout@v4
+      - name: Install Bun
+        run: |
+          curl -fsSL https://bun.sh/install | bash
+          echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
       - run: bun install --frozen-lockfile
       - run: bun run typecheck
       - run: bun run test