Disable the `LIMIT 1` in pg_get_constraintdef #153

Job	Run time
build	5m 30s
test	2h 43m 49s
test (--rollback-and-test)	2h 40m 26s
test (--rollback-and-reapply, -k test_link_on_target_delete -k test_edgeql_select -k test_dump)	28m 57s
Notify in Slack on failures	0s
	5h 58m 42s

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