Install yarn manually on Linux

azure-pipelines.yml

@@ -12,9 +12,15 @@ jobs:
     inputs:
       versionSpec: '8.x'
     displayName: 'Install Node.js'
+  - script: |
+      curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
+      echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
+      sudo apt-get update && sudo apt-get install yarn
+      sudo apt-get install --no-install-recommends yarn
+    displayName: 'Install yarn'
   - script: |
       yarn install
-    displayName: 'Install yarn dependencies'
+    displayName: 'Install npm dependencies'
   - script: |
       yarn tsc
     displayName: 'Build'