Bump unified_inventory from `3fffa41` to `8c84751`

Bumps [unified_inventory](https://github.com/minetest-mods/unified_inventory) from `3fffa41` to `8c84751`.
- [Release notes](https://github.com/minetest-mods/unified_inventory/releases)
- [Commits](https://github.com/minetest-mods/unified_inventory/compare/3fffa41eaf68ba749f276310f77da629821613f5...8c84751ff814ac5da75b1536bdf6961d9172b315)

unified_inventory @ 8c84751f

-Subproject commit 3fffa41eaf68ba749f276310f77da629821613f5
+Subproject commit 8c84751ff814ac5da75b1536bdf6961d9172b315