setup bun test workflow

.bun-version

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+1.1.38

.github/workflows/test.yml

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+name: Tests
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Setup Neovim
+      uses: rhysd/action-setup-vim@v1
+      with:
+        neovim: true
+        version: stable
+
+    - name: Setup Bun
+      uses: oven-sh/setup-bun@v2
+      with:
+        bun-version-file: ".bun-version"
+
+    - name: Install dependencies
+      working-directory: ./bun
+      run: bun install --frozen-lockfile
+
+    - name: Run tests
+      working-directory: ./bun
+      run: bun test