[build] downgrade kotlin to be compatible w/ideaVersion (#353)

* [build] downgrade kotlin to be compatible w/`ideaVersion`

* Updated comment

Author: pq

third_party/gradle.properties

@@ -16,6 +16,7 @@ pluginId = Dart
 pluginSinceBuild = 251
 pluginUntilBuild = 261.*
 
+# Tracking issue for changes required to bumpt to 2025.2.6.1: https://github.com/flutter/dart-intellij-third-party/issues/352
 ideaVersion = 2025.1.7
 
 javaVersion = 21

third_party/gradle/libs.versions.toml

@@ -4,7 +4,9 @@
 [versions]
 guava = "33.6.0-jre"
 junit = "4.13.2"
-kotlin = "2.3.21"
+# Bumping to 2.3.21 is blocked on an `ideaVersion` update: 
+# https://github.com/flutter/dart-intellij-third-party/issues/352
+kotlin = "2.2.21"
 intellijPlatform = "2.15.0"
 changelog = "2.5.0"
 kover = "0.9.8"