feat: [CBT-6 helper] Exposing Retry._deadline as a property (#20)

* Retry._deadline exposed as a property

* feat Retry._deadline exposed as a property

* added property test

Co-authored-by: q-logic <52290913+q-logic@users.noreply.github.com>
Co-authored-by: Christopher Wilcox <crwilcox@google.com>
diff --git a/google/api_core/retry.py b/google/api_core/retry.py
index a1d1f18..446d43c 100644
--- a/google/api_core/retry.py
+++ b/google/api_core/retry.py
@@ -288,6 +288,10 @@
 
         return retry_wrapped_func
 
+    @property
+    def deadline(self):
+        return self._deadline
+
     def with_deadline(self, deadline):
         """Return a copy of this retry with the given deadline.
 
diff --git a/tests/unit/test_retry.py b/tests/unit/test_retry.py
index be0c688..a0160e9 100644
--- a/tests/unit/test_retry.py
+++ b/tests/unit/test_retry.py
@@ -162,6 +162,7 @@
         assert retry_._multiplier == 2
         assert retry_._deadline == 120
         assert retry_._on_error is None
+        assert retry_.deadline == 120
 
     def test_constructor_options(self):
         _some_function = mock.Mock()