Install net9 sdk in signing pipeline test prebuild step (#3044)

Author: mdaigle

eng/pipelines/common/templates/steps/pre-build-step.yml

@@ -4,6 +4,18 @@
 # See the LICENSE file in the project root for more information.                #
 #################################################################################
 steps:
+- task: UseDotNet@2
+  displayName: 'Use .NET 9.x sdk'
+  inputs:
+    packageType: sdk
+    version: '9.x'
+
+- task: UseDotNet@2
+  displayName: 'Install .NET 8.x runtime'
+  inputs:
+    packageType: runtime
+    version: '8.x'
+
 - script: SET
   displayName: 'Print Environment Variables'