Use ubuntu-16.04

Author: athomas

.github/workflows/test-package.yml

@@ -37,7 +37,7 @@ jobs:
         if: always() && steps.install.outcome == 'success'
 
   # Run tests on a matrix consisting of two dimensions:
-  # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
+  # 1. OS: ubuntu-16.04
   # 2. release channel: dev
   test:
     needs: analyze
@@ -46,7 +46,7 @@ jobs:
       fail-fast: false
       matrix:
         # Add macos-latest and/or windows-latest if relevant for this package.
-        os: [ubuntu-latest]
+        os: [ubuntu-16.04]
         sdk: [dev]
     steps:
       - uses: actions/checkout@v2