Update Cosmos API to 26.3.build.19-alpha and upgrade Gradle to 9.8.0

plugin/build.gradle.kts

@@ -7,7 +7,7 @@ plugins {
 dependencies {
     // API
     implementation(project(":boosters-api"))
-    compileOnly("com.alttd.cosmos:cosmos-api:26.2.build.17-stable")
+    compileOnly("com.alttd.cosmos:cosmos-api:26.3.build.19-alpha")
     // MyPet
     compileOnly("de.keyle:mypet-api:4.0.1-SNAPSHOT")
     // mcMMO