test: Return root module root dir when using go.work

Previously, the helper returned all the output of `go list -m`,
and when using go.work, the output contains multiple lines, with
the directory of the root module on the first line.

Now, the helper returns only the first line.

Author: dlipovetsky

pkg/handlers/generic/lifecycle/ccm/nutanix/handler_test.go

@@ -209,5 +209,7 @@ func moduleRootDir() string {
 				out),
 		)
 	}
-	return strings.TrimSpace(string(out))
+	modules := strings.Split(string(out), "\n")
+	rootModule := strings.TrimSpace(modules[0])
+	return rootModule
 }