build(deps): bump org.jetbrains.kotlin:kotlin-gradle-plugin in /android

Bumps [org.jetbrains.kotlin:kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.9.10 to 1.9.20.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.10...v1.9.20)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

android/build.gradle

@@ -2,7 +2,7 @@ group 'dev.steenbakker.flutter_ble_peripheral'
 version '1.0-SNAPSHOT'
 
 buildscript {
-    ext.kotlin_version = '1.9.10'
+    ext.kotlin_version = '1.9.20'
     repositories {
         google()
         mavenCentral()