Bump velocity-api from 3.0.0-SNAPSHOT to 4.0.0-SNAPSHOT in /Plan

Bumps velocity-api from 3.0.0-SNAPSHOT to 4.0.0-SNAPSHOT.

---
updated-dependencies:
- dependency-name: com.velocitypowered:velocity-api
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Plan/build.gradle

@@ -77,7 +77,7 @@ subprojects {
         spongeVersion = "8.1.0"
         nukkitVersion = "1.0-SNAPSHOT"
         bungeeVersion = "1.16-R0.4"
-        velocityVersion = "3.0.0-SNAPSHOT"
+        velocityVersion = "4.0.0-SNAPSHOT"
         redisBungeeVersion = "0.3.8-SNAPSHOT"
         redisBungeeProxioDevVersion = "0.7.3"