fix: clear buffer on stmt retry

Signed-off-by: ekexium <eke@fastmail.com>

sessiontxn/isolation/base.go

@@ -222,6 +222,7 @@ func (p *baseTxnContextProvider) OnPessimisticStmtEnd(_ context.Context, _ bool)
 // OnStmtRetry is the hook that should be called when a statement is retried internally.
 func (p *baseTxnContextProvider) OnStmtRetry(ctx context.Context) error {
 	p.ctx = ctx
+	p.sctx.GetSessionVars().TxnCtx.CurrentStmtPessimisticLockCache = nil
 	return nil
 }