fix: improve get_partition_batches to treat integers properly

[nicor88]

Description

Our functional tests were failing. Specifically, the failures seem due only to cases where we deal with partitions and partitions being integers and it started with dbt-core==1.6.3.

An example of functional tests failing can be found here

In case we one partition that is an integer, adapter.convert_type returns None, not integer, as you can see from here.

This PR treats integers and None types equally - assuming that None types are actually integer.

This issue should be actually fixed in dbt-core, but for now we add this workaround.

Checklist

• You followed contributing section
• You kept your Pull Request small and focused on a single feature or bug fix.
• You added unit testing when necessary
• You added functional testing when necessary