Include JDK 20 in default EA list

[sormuras]

https://jdk.java.net/19/ entered RDP1, https://jdk.java.net/20/ will show up soon. Thus, the value part of the following line should start with "20,19,loom,...

setup-java/src/ListOpenJavaDevelopmentKits.java

Line 48 in 6f63b6c

static final String EA = System.getProperty("EA", "19,loom,metropolis,panama,valhalla");