Update netbeans to 12.6, since that's the only supported version and the download link has changed, causing build failures anyway

gradle.properties

@@ -14,4 +14,4 @@ buildJavaDoc = true
 buildSdkProject = true
 
 # Path for downloading NetBeans Base
-netbeansUrl = https://downloads.apache.org/netbeans/netbeans/12.0/netbeans-12.0-bin.zip
+netbeansUrl = https://downloads.apache.org/netbeans/netbeans/12.6/netbeans-12.6-bin.zip