reorder includes to avoid Boost L conflict

[Habbie]

Short description

See #6542, #6516, #6358.

This is an alternative to #6517 which could still be merged eventually.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[rgacogne]

I'm torn because #6517 is a big diff, which feels wrong for a minor release, but it would make backporting things from master much easier in the future.

[Habbie]

I'm torn because #6517 is a big diff, which feels wrong for a minor release, but it would make backporting things from master much easier in the future.

We had the same discussion on the auth side last week - but there we really wanted to release so we went for the shorter one. As said, the longer one can still go in later. I am also torn on it, and indeed it has caused me trouble in backporting a few times already.