Kotlin: enable 2.4.20-RC support

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: andersfugmann

java/kotlin-extractor/versions.bzl

@@ -12,6 +12,7 @@ VERSIONS = [
     "2.3.0",
     "2.3.20",
     "2.4.0",
+    "2.4.20-RC",
 ]
 
 def _version_to_tuple(v):

java/ql/integration-tests/kotlin/all-platforms/diagnostics/kotlin-version-too-new/diagnostics.expected

@@ -1,5 +1,5 @@
 {
-  "markdownMessage": "The Kotlin version installed (`999.999.999`) is too recent for this version of CodeQL. Install a version lower than 2.4.20.",
+  "markdownMessage": "The Kotlin version installed (`2.4.20`) is too recent for this version of CodeQL. Install a version lower than 2.4.20.",
   "severity": "error",
   "source": {
     "extractorName": "java",

java/ql/integration-tests/kotlin/all-platforms/diagnostics/kotlin-version-too-new/fake-kotlinc-source/kotlin/KotlinVersion.java

@@ -2,6 +2,6 @@
 
 public class KotlinVersion {
 
-  public static String CURRENT = "999.999.999";
+  public static String CURRENT = "2.4.20";
 
 }