Bump org.spigotmc:spigot-api

Bumps org.spigotmc:spigot-api from 1.20.6-R0.1-SNAPSHOT to 1.21.1-R0.1-SNAPSHOT.

---
updated-dependencies:
- dependency-name: org.spigotmc:spigot-api
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle.kts

@@ -33,7 +33,7 @@ dependencies {
 
     // Other dependencies that are not required or already available at runtime
     compileOnly("org.projectlombok:lombok:1.18.34")
-    compileOnly("org.spigotmc:spigot-api:1.20.6-R0.1-SNAPSHOT")
+    compileOnly("org.spigotmc:spigot-api:1.21.1-R0.1-SNAPSHOT")
     compileOnly("com.github.MilkBowl:VaultAPI:1.7")
     compileOnly("me.clip:placeholderapi:2.11.6")
     compileOnly("dev.rosewood:rosestacker:1.5.24")