Fix mssql 2017 integration test (elixir-ecto#635)

Author: greg-rychlewski

.github/workflows/ci.yml

@@ -83,7 +83,7 @@ jobs:
 
   test-mssql:
     name: mssql integration test
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix: