Fixes a typo in tablecmd

Hi Hackers,

I noticed this while working on a patch with tablecmd:

```
/*
* If the table at either end of the constraint is partitioned, we need to
* recurse and handle every unvalidate constraint that is a child of this
* constraint.
*/
```

Here “unvalidate” looks abnormal to me but not an obvious spelling error.
Then I searched over the source tree, and found two similar occurrences:

Also in tablecmd.c
```
/* an unvalidated constraint is no good */
```

In pg_dump.c
```
/*
* An unvalidated constraint needs to be dumped separately, so
* that potentially-violating existing data is loaded before
* the constraint.
*/
```

Notice the difference: “unvalidate” vs “unvalidated”.

Then I recalled that Tom referred to the online dictionary
https://www.onelook.com for checking typo in discussion [1], and I checked
with the web site. It shows that “unvalidate” is not found; and
“unvalidated” has 3 matches and means “not confirmed as true yet”.

So, I believe “unvalidate” is a typo, a “d” should be appended.

[1] https://postgr.es/m/2118725.1762837193@sss.pgh.pa.us

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/