Remove from option for JDK 20 on GitHub action

Otherwise the build fails on CI

Author: DavideD

.github/workflows/build.yml

@@ -150,7 +150,7 @@ jobs:
           # We want to enable preview features when testing newer builds of OpenJDK:
           # even if we don't use these features, just enabling them can cause side effects
           # and it's useful to test that.
-          - { name: "20", java_version_numeric: 20, from: 'jdk.java.net', jvm_args: '--enable-preview' }
+          - { name: "20", java_version_numeric: 20, jvm_args: '--enable-preview' }
           - { name: "21-ea", java_version_numeric: 21, from: 'jdk.java.net', jvm_args: '--enable-preview' }
           - { name: "22-ea", java_version_numeric: 22, from: 'jdk.java.net', jvm_args: '--enable-preview' }
     steps: