config: reduce zero-copy space reserve default

tests/test_config.py

@@ -34,6 +34,7 @@ class ConfigTests(unittest.TestCase):
                 root / "qb/a/b",
             )
             self.assertEqual(config.jobs.stall_after, 30 * 60)
+            self.assertEqual(config.jobs.free_space_reserve_bytes, 32 * 1024 * 1024)
             self.assertEqual(
                 config.syncthing.advertised_addresses, ("dynamic",)
             )

tests/test_jobs.py

@@ -74,7 +74,7 @@ class ClientJobHappyPathTests(unittest.TestCase):
             self._run_transfer(
                 Path(directory),
                 job_pb2.JOB_OPERATION_ARCHIVE,
-                source_stage_free_bytes=1024 * 1024 * 1024 + 1024,
+                source_stage_free_bytes=32 * 1024 * 1024 + 1024,
                 content=b"x" * 4096,
             )