enable portaudio installation by existence of a variable that we will set in the matrix for portaudio ci.yml (#42693)

Author: scbedd

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

@@ -0,0 +1,11 @@
+steps:
+  - script: |
+      if [[ "$AGENT_OS" == "Linux" ]]; then
+        sudo apt-get update
+        sudo apt-get install -y portaudio19-dev libasound2-dev
+      elif [[ "$AGENT_OS" == "Darwin" ]]; then
+        brew update
+        brew install portaudio
+      fi
+    displayName: Install portaudio dependencies if necessary
+    condition: and(succeeded(), ne(variables['InstallPortAudio'], ''), or(eq(variables['Agent.OS'], 'Linux'), eq(variables['Agent.OS'], 'Darwin')))

eng/pipelines/templates/steps/use-venv.yml

@@ -42,4 +42,6 @@ steps:
           -VenvName "${{ parameters.VirtualEnvironmentName }}" `
           -RepoRoot "$(Build.SourcesDirectory)"
       displayName: Use ${{ parameters.VirtualEnvironmentName }} Virtual Environment
-      condition: ${{ parameters.Condition }}
+      condition: ${{ parameters.Condition }}
+
+    - template: install-portaudio.yml