test_db/test_db_copy_to: Fix hypothesis FailedHealthCheck error

With latest version of hypothesis, this test often raises the following
error:

hypothesis.errors.FailedHealthCheck: Data generation is extremely slow ...

Setting the number of hypothesis examples for that test to a lower value
makes the error goes away.

This should also fix that test execution in the swh-environment/tests
Jenkins job which often fails.

swh/core/db/tests/test_db.py

@@ -290,7 +290,7 @@ def test_db_copy_to_static(db_with_data):
         assert EXPECTED_ROW_OUT == output[0]
 
 
-@settings(suppress_health_check=function_scoped_fixture_check)
+@settings(suppress_health_check=function_scoped_fixture_check, max_examples=5)
 @given(db_rows)
 def test_db_copy_to(db_with_data, data):
     items = [dict(zip(COLUMNS, item)) for item in data]