[Tools] Update .NET SDK Versions (#9530)

* [Tools] Update .NET SDK Versions

The focus of these changes is to update the .NET SDK versions used in the
pipelines to include the latest. This will allow testing on the current platform.

eng/pipelines/templates/steps/install-dotnet.yml

@@ -9,10 +9,10 @@ steps:
     inputs:
       useGlobalJson: true
 
-  # We install .NET 6.0.x SDK in addition to .NET coming from global.json because most of our tools target 6.0.x.
+  # We install .NET 8.0.x SDK in addition to .NET coming from global.json because most of our tools target 8.0.x.
   # Once we migrate all tools to a newer .NET version, we should update this to install that version instead.
   - task: UseDotNet@2
-    displayName: "Use .NET SDK 6.0.x"
+    displayName: "Use .NET SDK 8.0.x"
     retryCountOnTaskFailure: 3
     inputs:
       # We must install sdk, not just runtime, as it is required by some of our tools, like test-proxy.
@@ -23,7 +23,7 @@ steps:
       # https://github.com/Azure/azure-sdk-tools/pull/5405#discussion_r1105006774
       # https://github.com/Azure/azure-sdk-tools/pull/5405
       packageType: sdk
-      version: 6.0.x
+      version: 9.0.x
       # performMultiLevelLookup comes into play when given .NET executable target runtime is different
       # than the installed .NET SDK. Without this, such runtime would not be found.
       performMultiLevelLookup: true