Bump Kotlin to Flutter's minimum

Used to be 1.5.20

Author: validcube

system_theme/android/build.gradle

@@ -2,7 +2,7 @@ group 'com.bruno.system_theme'
 version '1.0-SNAPSHOT'
 
 buildscript {
-    ext.kotlin_version = '1.5.20'
+    ext.kotlin_version = '1.7.0'
     repositories {
         google()
         jcenter()