feat: Updates to .NET 9 (#1984)

### Summary

* Bumps to .NET 9 with updated dependencies
* Comparing a value type against null is no longer allowed
* CI/CD now uses the version specified in global.json
* Serialization generator updated to .NET 9 with bug fixes, fixes to turkish language, and parallelization

.github/workflows/build-test.yml

@@ -23,10 +23,10 @@ jobs:
     - uses: actions/checkout@v4
       with:
         fetch-depth: 0 # avoid shallow clone so nbgv can do its work.
-    - name: Setup .NET 8
+    - name: Install .NET 9
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 8.0.x
+        global-json-file: global.json
     - name: Install Prerequisites
       run: |
         brew update
@@ -86,10 +86,10 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0 # avoid shallow clone so nbgv can do its work.
-      - name: Setup .NET 8
+      - name: Install .NET 9
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: 8.0.x
+          global-json-file: global.json
       - name: Build
         run: ./publish.cmd Release
       - name: Test