ImportGramplet: look up imported person by handle, not gramps_id

The death-fallback test fetched the imported person with
get_person_from_gramps_id("I00001"), but core's XML importer normalises
gramps_ids to the database's configured width — under the default "I%04d"
the fixture's "I00001" becomes "I0001" — so the literal lookup returned
None and the test failed on every default-config tree (reported by
GaryGriffin on macOS; reproduced here against maintenance/gramps60 and on
Linux).

Exactly one person is imported, so fetch it by handle instead. This removes
the dependency on gramps_id formatting; the death/birth assertions already
resolve their events by handle. The fix wiring under test is unchanged — the
death_ref is correctly set on clean XML, confirming bug 13420 does not
reproduce on conformant input.

Verified: 1 test OK against maintenance/gramps60 (direct unittest and
gramps-testbed addon-unit runner).

Bug #13420

Author: eduralph

ImportGramplet/tests/test_xml_death_fallback.py

@@ -154,11 +154,16 @@ def test_clean_xml_imports_set_death_ref_via_atomic_parser(self):
         ifile = BytesIO(CLEAN_XML.encode("utf-8"))
         parser.parse(ifile)
 
-        person = self.database.get_person_from_gramps_id("I00001")
-        self.assertIsNotNone(
-            person,
-            "Person I00001 must exist after XML import",
+        # Look the person up by handle, not by gramps_id: core's importer
+        # normalises gramps_ids to the database's configured width (the XML
+        # "I00001" becomes "I0001" under the default "I%04d"), so a literal
+        # gramps_id lookup is brittle and fails on any default-config tree.
+        # Exactly one person was imported, so fetch it directly.
+        handles = list(self.database.get_person_handles())
+        self.assertEqual(
+            len(handles), 1, "exactly one person must be imported"
         )
+        person = self.database.get_person_from_handle(handles[0])
 
         death_ref = person.get_death_ref()
         self.assertIsNotNone(