tikv/unistore can't handle sql mode and get wrong sql result

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
tidb> drop table t;
Query OK, 0 rows affected (0.23 sec)

tidb> create table t(a varchar(100), b varchar(100));
Query OK, 0 rows affected (0.10 sec)

tidb> insert into t values("2000-00-00", "%Y-%m-%d");
Query OK, 1 row affected (0.02 sec)

tidb> select str_to_date(a,b) from t where str_to_date(a,b) is not null;
+----------------------------+
| str_to_date(a,b) |
+----------------------------+
| NULL |
+----------------------------+
1 rows in set, 1 warning (0.01 sec)
```

### 2. What did you expect to see? (Required)

### 3. What did you see instead (Required)

### 4. What is your TiDB version? (Required)
master

### Analyse:
Add a log in the function str_to_date. Run tidb + unistore
```
diff --git a/pkg/expression/builtin_time_vec.go b/pkg/expression/builtin_time_vec.go
index e563d0221b..7775871e5e 100644
--- a/pkg/expression/builtin_time_vec.go
+++ b/pkg/expression/builtin_time_vec.go
@@ -26,7 +26,9 @@ import (
"github.com/pingcap/tidb/pkg/types"
"github.com/pingcap/tidb/pkg/util"
"github.com/pingcap/tidb/pkg/util/chunk"
+ "github.com/pingcap/tidb/pkg/util/logutil"
"github.com/tikv/client-go/v2/oracle"
+ "go.uber.org/zap"
)

func (b *builtinMonthSig) vecEvalInt(ctx EvalContext, input *chunk.Chunk, result *chunk.Column) error {
@@ -1493,6 +1495,7 @@ func (b *builtinStrToDateDatetimeSig) vecEvalTime(ctx EvalContext, input *chunk.
times := result.Times()
tc := typeCtx(ctx)
hasNoZeroDateMode := sqlMode(ctx).HasNoZeroDateMode()
+ logutil.BgLogger().Error("builtinStrToDateDatetimeSig", zap.Any("hasNoZeroDateMode", hasNoZeroDateMode), zap.Stack(""))
fsp := b.tp.GetDecimal()

for i := 0; i < n; i++ {
```
And run the sql, we can see unistore can't handle the sqlmode.