inserting null on an autoincrement primary key prevents cleanup

When I have a table with a primary key column that's also increment, it's valid to set it to `null` on the insert statement. the last insert it will then return the auto increment value, which is the primary key in that case.

As already noticed in #44, the auto increment column doesn't have to be part of the primary key, so the return value of last insert id ironically doesn't necessarily belong to the primary key. However, #44 also broke the case, which one might perceive as more common, that the last insert id may also be the primary key.

So, `haveInDatabase(table, ['id' => null, ...])` with id as autoincrement and pk will lead to the id being set to `null` for cleanup, which results in the row not being removed at teardown.

I have prepared a fix for this case, which hopefully is specific enough to not interfere with other use cases.

先使用自動遞增主鍵重現 haveInDatabase(table, ['id' => null, ...]) 的情況，然後追蹤插入的 ID 如何為 teardown cleanup 記錄。完成的標準是保留產生的主鍵值，並在 cleanup 期間移除插入的資料列，同時不破壞自動遞增欄位不是主鍵的情況。

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