postgres: update pgpass path on windows

[joeydewaal]

Does your PR solve an issue?

fixes #4097

The creator of the issue added a link to the libpq source code (thanks!), which was used to create this pr (https://github.com/postgres/postgres/blob/master/src/interfaces/libpq/fe-connect.c#L8262).

Is this a breaking change?

Behavior changes can be breaking if significant enough. Consider Hyrum's Law:

With a sufficient number of users of an API,
it does not matter what you promise in the contract:
all observable behaviors of your system
will be depended on by somebody.

No, no public api is changed. However, this does change the behavior of loading in a pgpass file on windows.