fix(docs): build cli for e2e tests (#24184)

docs/docs/developer/testing.md

@@ -18,6 +18,7 @@ make e2e
 Before you can run the tests, you need to run the following commands _once_:
 
 - `pnpm install` (in `e2e/`)
+- `pnpm run build` (in `cli/`)
 - `make open-api` (in the project root `/`)
 
 Once the test environment is running, the e2e tests can be run via: