Gradle build failure with openjdk 16 due to groovy version incompatability

[planetf1]

$ ./gradlew build                                                                                          [12:05:06]
Picked up JAVA_TOOL_OPTIONS: --add-exports=java.naming/com.sun.jndi.ldap=ALL-UNNAMED
Starting a Gradle Daemon (subsequent builds will be faster)

FAILURE: Build failed with an exception.

* Where:
Build file '/Users/jonesn/IdeaProjects/egeria.maven/build.gradle'

* What went wrong:
Could not compile build file '/Users/jonesn/IdeaProjects/egeria.maven/build.gradle'.
> startup failed:
  General error during semantic analysis: Unsupported class file major version 60

  java.lang.IllegalArgumentException: Unsupported class file major version 60
        at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:196)
        at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:177)
        at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:163)
        at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:284)
        at org.codehaus.groovy.ast.decompiled.AsmDecompiler.parseClass(AsmDecompiler.java:81)
        at org.codehaus.groovy.control.ClassNodeResolver.findDecompiled(ClassNodeResolver.java:251)
        at org.codehaus.groovy.control.ClassNodeResolver.tryAsLoaderClassOrScript(ClassNodeResolver.java:189)
        at org.codehaus.groovy.control.ClassNodeResolver.findClassNode(ClassNodeResolver.java:169)
        at org.codehaus.groovy.control.ClassNodeResolver.resolveName(ClassNodeResolver.java:125)
        at org.codehaus.groovy.ast.decompiled.AsmReferenceResolver.resolveClassNullable(AsmReferenceResolver.java:57)

We do not see issues with maven - which uses groovy for FVTs, but this appears to be gradle itself

We are currently running gradle 6.8.3:

$ ./gradlew -version                                                                                       [12:09:38]
Picked up JAVA_TOOL_OPTIONS: --add-exports=java.naming/com.sun.jndi.ldap=ALL-UNNAMED

------------------------------------------------------------
Gradle 6.8.3
------------------------------------------------------------

Build time:   2021-02-22 16:13:28 UTC
Revision:     9e26b4a9ebb910eaa1b8da8ff8575e514bc61c78

Kotlin:       1.4.20
Groovy:       2.5.12
Ant:          Apache Ant(TM) version 1.10.9 compiled on September 27 2020
JVM:          11.0.11 (Azul Systems, Inc. 11.0.11+9-LTS)
OS:           Mac OS X 11.4 x86_64

[planetf1]

The groovy issue itself can be resolved by moving to gradle 7, which supports openjdk 16.
However gradle 7 adds further validation on task attributes, which currently the execfork plugin we use fails on - issue opened on that project,.