Update GitHub Actions to latest action versions

Upgraded actions in ci.yml:
- checkout: v4 → v6
- setup-dotnet: v4 → v5
- upload-artifact: v4 → v7
- download-artifact: v4 → v8

Applied to both test-standard and test-explicit jobs.

Author: kzdev-net

.github/workflows/ci.yml

@@ -13,10 +13,10 @@ jobs:
     timeout-minutes: 30
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v5
         with:
           dotnet-version: 10.x
 
@@ -30,7 +30,7 @@ jobs:
         run: dotnet test Source/KZDev.PerfUtils.slnx -c Release --no-build
 
       - name: Upload Release artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: test-release-artifacts
           path: artifacts
@@ -46,15 +46,15 @@ jobs:
     continue-on-error: ${{ (github.event_name == 'pull_request' && github.base_ref != 'main') || (github.event_name == 'push' && github.ref == 'refs/heads/dev') }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v5
         with:
           dotnet-version: 10.x
 
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: test-release-artifacts
           path: artifacts