chore: bump GitHub Actions versions

- actions/checkout v4 -> v6
- actions/setup-python v5 -> v6
- actions/setup-dotnet v4 -> v5
- actions/upload-pages-artifact v3 -> v4

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: fa-yoshinobu

.github/workflows/ci.yml

@@ -15,10 +15,10 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup .NET SDK
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v5
         with:
           dotnet-version: 9.0.x
 
@@ -53,7 +53,7 @@ jobs:
 
       - name: Upload pages artifact
         if: github.ref == 'refs/heads/main'
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v4
         with:
           path: docs/
 

.github/workflows/release.yml

@@ -9,8 +9,8 @@ jobs:
   package:
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-dotnet@v4
+      - uses: actions/checkout@v6
+      - uses: actions/setup-dotnet@v5
         with: { dotnet-version: 9.0.x }
       - name: Restore
         run: dotnet restore