Fix codecov.io upload on Windows (#3360)

Author: crusaderky

ci/azure/unit-tests.yml

@@ -19,7 +19,8 @@ steps:
   displayName: Run tests
 
 - bash: |
-    bash <(curl https://codecov.io/bash) -t 688f4d53-31bb-49b5-8370-4ce6f792cf3d
+    curl https://codecov.io/bash > codecov.sh
+    bash codecov.sh -t 688f4d53-31bb-49b5-8370-4ce6f792cf3d
   displayName: Upload coverage to codecov.io
 
 # TODO: publish coverage results to Azure, once we can merge them across