Bump actions/checkout from v4 to v6 in release workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: suma

.github/workflows/release.yml

@@ -13,7 +13,7 @@ jobs:
     name: Test
     runs-on: macos-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: Swatinem/rust-cache@v2
       - name: Run tests
         run: cargo test
@@ -33,7 +33,7 @@ jobs:
             runner: windows-latest
             os: windows
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: Swatinem/rust-cache@v2
         with:
@@ -83,7 +83,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download all artifacts
         uses: actions/download-artifact@v4