System properties in native-gradle-plugin should be wrapped in double quotes

[wirthi]

System properties propagated to java from native-gradle-plugin system properties configuration are wrapped in quotes

graalvmNative {
  binaries {
    main {     
      systemProperties = [propertyName: 'value']

System.getProperty("propertyName") in java then returns a 7 character string starting and ending with a double-quote character - "value"

(note: reported as GR-60693 to GraalVM and copied here)