deps: bump com.github.retrooper:packetevents-spigot from 2.9.1 to 2.9.4 (#558)

Bumps [com.github.retrooper:packetevents-spigot](https://github.com/retrooper/packetevents) from 2.9.1 to 2.9.4.
- [Release notes](https://github.com/retrooper/packetevents/releases)
- [Changelog](https://github.com/retrooper/packetevents/blob/2.0/CHANGELOG.md)
- [Commits](https://github.com/retrooper/packetevents/compare/v2.9.1...v2.9.4)

---
updated-dependencies:
- dependency-name: com.github.retrooper:packetevents-spigot
  dependency-version: 2.9.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

bukkit/build.gradle

@@ -21,7 +21,7 @@ dependencies {
     implementation 'de.tr7zw:item-nbt-api:2.15.2-SNAPSHOT'
 
     compileOnly "io.papermc.paper:paper-api:${paper_api_version}"
-    compileOnly 'com.github.retrooper:packetevents-spigot:2.9.1'
+    compileOnly 'com.github.retrooper:packetevents-spigot:2.9.4'
     compileOnly 'com.github.dmulloy2:ProtocolLib:5.3.0'
     compileOnly 'org.projectlombok:lombok:1.18.38'
     compileOnly 'commons-io:commons-io:2.19.0'