test: set pool.provider= on mocks to avoid MagicMock truthy guard trigger

The provider-mismatch guard now checks pool_provider and
current_provider != pool_provider. MagicMock.provider returns
a truthy child mock by default, which would trigger the guard
and skip the pool recovery tests. Set pool.provider='' explicitly.

tests/agent/test_credential_pool_routing.py

@@ -155,6 +155,9 @@ class TestPoolRotationCycle:
 
         pool = MagicMock()
         pool.has_credentials.return_value = True
+        # Must be set explicitly — MagicMock.provider returns a truthy
+        # child mock, which would trigger the provider-mismatch guard.
+        pool.provider = ""
 
         # mark_exhausted_and_rotate returns next entry until exhausted
         self._rotation_index = 0

tests/run_agent/test_credential_pool_interrupt.py

@@ -27,6 +27,9 @@ def _make_pool(entries):
     pool = MagicMock()
     pool.entries = entries
     pool.current.return_value = entries[0]
+    # Must be set explicitly — MagicMock.provider returns a truthy
+    # child mock, which would trigger the provider-mismatch guard.
+    pool.provider = ""
     return pool