Remove deprecated Gradle features from QtJenny

> Task :compiler:compileKotlin
w: file:///home/rami/dev/tmp/QTBUG-131703/qtjennyagain/qtjenny/compiler/src/main/java/org/qtproject/qt/qtjenny/HandyHelper.kt:130:56 'toLowerCase(Locale): String' is deprecated. Use lowercase() instead.
w: file:///home/rami/dev/tmp/QTBUG-131703/qtjennyagain/qtjenny/compiler/src/main/java/org/qtproject/qt/qtjenny/HandyHelper.kt:303:20 'toLowerCase(Locale): String' is deprecated. Use lowercase() instead.
w: file:///home/rami/dev/tmp/QTBUG-131703/qtjennyagain/qtjenny/compiler/src/main/java/org/qtproject/qt/qtjenny/HandyHelper.kt:307:23 'capitalize(): String' is deprecated. Use replaceFirstChar instead.
w: file:///home/rami/dev/tmp/QTBUG-131703/qtjennyagain/qtjenny/compiler/src/main/java/org/qtproject/qt/qtjenny/HandyHelper.kt:324:49 'toLowerCase(Locale): String' is deprecated. Use lowercase() instead.
w: file:///home/rami/dev/tmp/QTBUG-131703/qtjennyagain/qtjenny/compiler/src/main/java/org/qtproject/qt/qtjenny/HandyHelper.kt:328:51 'toLowerCase(Locale): String' is deprecated. Use lowercase() instead.
 
Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.
 
You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.
 
For more on this, please refer to https://docs.gradle.org/8.7/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.