sql: step read committed txn on statement retry

This commit steps a read committed transaction's read sequence after
each statement retry. This ensures that the read sequence leads the
ignored sequence number range established when the read committed
statement savepoint was rolled back.

Epic: None
Release note: None

pkg/sql/conn_executor_exec.go

@@ -1755,6 +1755,9 @@ func (ex *connExecutor) dispatchReadCommittedStmtToExecutionEngine(
 		if err := ex.state.mu.txn.PrepareForPartialRetry(ctx); err != nil {
 			return err
 		}
+		if err := ex.state.mu.txn.Step(ctx, false /* allowReadTimestampStep */); err != nil {
+			return err
+		}
 		ex.state.mu.autoRetryCounter++
 		ex.state.mu.autoRetryReason = txnRetryErr
 	}