fix: Specific guns now have correct copy-from to fix their weapon categories.

[KheirFerrum]

Purpose of change

A long time ago someone on the discord noted that several guns have the wrong categories applied, I checked and agreed, and changed the copy-from so that they now point at the right category.

Describe the solution

Change copy-from for the following guns.

• Mossberg Brownie: pistol_base -> pistol_1shot
• SKS: rifle_manual -> rifle_semi
• Pipe Shotgun: shotgun_base -> shotgun_1shot
• M1897 Trench Gun: shotgun_base -> shotgun_pump

Describe alternatives you've considered

Leaving it alone until someone points it out again.

Testing

Load up the game, check that:

• Mossberg Brownie is now in One Shot category
• SKS is now in Autoloading category
• Pipe Shotgun is now in One Shot category.
• M1897 Trench Gun is now in Manual Action category

Additional context

I made derringers count as 1 shot guns due to their barrel arrangement, we could probably make them into another abstract that uses manual action to separate them from true 1shot guns that lack any kind of rotating firing pin or similar mechanism.

Checklist