sweepbatcher: fix flaky test

Since bb837a4aec AddSweep loads sweeps so
one of possible errors is sql.ErrTxDone. Full error that is fixed:
> fetchSweeps failed: failed to load sweep 0000000000000000000101:1:
> failed to fetch sweep data for 010101000000:
> failed to fetch loop out for 010101000000:
> sql: transaction has already been committed or rolled back

sweepbatcher/sweep_batcher_test.go

@@ -2,6 +2,7 @@ package sweepbatcher
 
 import (
 	"context"
+	"database/sql"
 	"errors"
 	"fmt"
 	"os"
@@ -3997,6 +3998,9 @@ func testSweepBatcherCloseDuringAdding(t *testing.T, store testStore,
 			if errors.Is(err, context.Canceled) {
 				break
 			}
+			if errors.Is(err, sql.ErrTxDone) {
+				break
+			}
 			require.NoError(t, err)
 		}
 	}()