fix: do not render timestamp precision when unspecified (#5709)
[TML-1647](https://linear.app/prisma-company/issue/TML-1647/fix-broken-citext-integration-test)
[MySQL docs
state](https://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html):
> If a
[TIMESTAMP](https://dev.mysql.com/doc/refman/5.7/en/datetime.html) or
[DATETIME](https://dev.mysql.com/doc/refman/5.7/en/datetime.html) column
definition includes an explicit fractional seconds precision value
anywhere, the same value must be used throughout the column definition.
This is permitted:
```
CREATE TABLE t1 (
ts TIMESTAMP(6) DEFAULT CURRENT_TIMESTAMP(6) ON UPDATE CURRENT_TIMESTAMP(6)
);
```
> This is not permitted:
```
CREATE TABLE t1 (
ts TIMESTAMP(6) DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP(3)
);
```
Fixes https://github.com/prisma/prisma/issues/28873