Run E2E tests from durabletask-go main branch instead of latest

Author: cgillum

.github/workflows/pr-validation.yml

@@ -45,6 +45,6 @@ jobs:
     # Install and run the durabletask-go sidecar for running e2e tests
     - name: Pytest e2e tests
       run: |
-        go install github.com/microsoft/durabletask-go@latest
+        go install github.com/microsoft/durabletask-go@main
         durabletask-go --port 4001 &
         pytest -m "e2e" --verbose