Bump org.spigotmc:spigot-api (#16)

Author: dependabot[bot]

build.gradle.kts

@@ -44,7 +44,7 @@ repositories {
 val adventureVersion = "4.16.0"
 
 dependencies {
-    compileOnly("org.spigotmc:spigot-api:1.20.4-R0.1-SNAPSHOT")
+    compileOnly("org.spigotmc:spigot-api:1.21.1-R0.1-SNAPSHOT")
 
     compileOnly("org.apache.commons:commons-lang3:3.16.0")
     compileOnly("org.projectlombok:lombok:1.18.32")