Bump CI actions to Node 24 majors to clear runner deprecation warning

GitHub Actions runners deprecated Node 20 and annotate every run that
uses a node20 action. checkout v4, setup-dotnet v4, and upload-artifact
v4 all run on node20, so bump each to its current major:

- actions/checkout v4 -> v7 (Node 24 since v5; v6/v7 changes do not
  affect this workflow's usage)
- actions/setup-dotnet v4 -> v6 (Node 24 since v5; global.json's
  fully-qualified sdk.version satisfies the stricter v5.4 validation)
- actions/upload-artifact v4 -> v7 (Node 24 default since v6; the
  name/path inputs used here are unchanged)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: lgamorim

.github/workflows/ci.yml

@@ -15,10 +15,10 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v6
         with:
           global-json-file: global.json
 
@@ -38,7 +38,7 @@ jobs:
         run: dotnet pack --configuration Release --no-build --output artifacts
 
       - name: Upload NuGet artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: nuget-packages
           path: artifacts/*.nupkg
@@ -48,10 +48,10 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v6
         with:
           global-json-file: global.json