Bump actions/checkout from 4 to 6 - #16

Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires pocketmine/pocketmine-mp 5.0.0 (exact version match: 5.0.0 or 5.0.0.0), found pocketmine/pocketmine-mp[5.0.0] but these were not loaded, because they are affected by security advisories. To ignore the advisories, add ("PKSA-gsjv-vrbx-n6br", "PKSA-1y47-vhgh-zq2y", "PKSA-krv9-c6mg-smc2", "PKSA-7cft-g1hs-ddc8", "PKSA-nv2r-zxzd-wzsw", "PKSA-w66x-n614-p3z6") to the audit "ignore" config. To turn the feature off entirely, you can set "block-insecure" to false in your "audit" config.