chore(generator): restore get_uuid4_re macro in test_macros.j2

Author: hebaalazzeh

packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2

@@ -2215,6 +2215,10 @@ def test_initialize_client_w_{{transport_name}}():
 {% endfor %}{# method in service.methods.values() #}
 {% endmacro %}{# empty_call_test #}
 
+{% macro get_uuid4_re() -%}
+{{ uuid4_re }}
+{%- endmacro %}{# uuid_re #}
+
 {% macro routing_parameter_test(service, api, transport, is_async) %}
 {% for method in service.methods.values() %}{# method #}
 {# See existing proposal b/330610501 to add support for explicit routing in BIDI/client side streaming #}