xtext: Bad Platform artifacts show up in build

in the builds with Java 8

https://github.com/itemis/xtext-reference-projects/runs/2835856963?check_suite_focus=true https://github.com/itemis/xtext-reference-projects/runs/2835856620?check_suite_focus=true

new plaform artifacts seem to be pulled this leads to build failing

 * What went wrong:
Execution failed for task ':org.xtext.example.mydsl:generateXtext'.
> com.google.common.util.concurrent.ExecutionError: com.google.common.util.concurrent.ExecutionError: com.google.common.util.concurrent.ExecutionError: com.google.common.util.concurrent.ExecutionError: com.google.common.util.concurrent.ExecutionError: java.lang.UnsupportedClassVersionError: org/eclipse/core/runtime/OperationCanceledException has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

2021-06-16T04:48:23.8460022Z 1    ERROR Mwe2Launcher       - org/eclipse/core/runtime/OperationCanceledException has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
2021-06-16T04:48:23.8465375Z java.lang.UnsupportedClassVersionError: org/eclipse/core/runtime/OperationCanceledException has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
2021-06-16T04:48:23.8469044Z 	at java.lang.ClassLoader.defineClass1(Native Method)
2021-06-16T04:48:23.8471712Z 	at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
2021-06-16T04:48:23.8474734Z 	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
2021-06-16T04:48:23.8477789Z 	at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
2021-06-16T04:48:23.8480558Z 	at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
2021-06-16T04:48:23.8483125Z 	at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
2021-06-16T04:48:23.8486274Z 	at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
2021-06-16T04:48:23.8489455Z 	at java.security.AccessController.doPrivileged(Native Method)
2021-06-16T04:48:23.8492711Z 	at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
2021-06-16T04:48:23.8495707Z 	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
2021-06-16T04:48:23.8508810Z 	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
2021-06-16T04:48:23.8513500Z 	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Launcher.run(Mwe2Launcher.java:74)
2021-06-16T04:48:23.8518115Z 	at org.eclipse.emf.mwe2.launch.runtime.Mwe2Launcher.main(Mwe2Launcher.java:37)
2021-06-16T04:48:23.8523737Z 	at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:254)
2021-06-16T04:48:23.8527488Z 	at java.lang.Thread.run(Thread.java:748)