gui: mockito/bytebudy warning about breaking in future jdk versions

[Tom-Willemsen]

Issue Description

22:18:08  Mockito is currently self-attaching to enable the inline-mock-maker. This will no longer work in future releases of the JDK. Please add Mockito as an agent to your build what is described in Mockito's documentation: https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#0.3
22:18:09  22:18:09.609 [SetInstrument thread] INFO  uk.ac.stfc.isis.ibex.preferences.PreferenceSupplier - getDefaultPythonPath found python at: C:\Instrument\Apps\Python3\python.exe
22:18:10  WARNING: A Java agent has been loaded dynamically (E:\Jenkins\workspace\releases_pipeline_Release_25.2.0\build\.m2\net\bytebuddy\byte-buddy-agent\1.15.2\byte-buddy-agent-1.15.2.jar)
22:18:10  WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
22:18:10  WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
22:18:10  WARNING: Dynamic loading of agents will be disallowed by default in a future release
22:18:10  OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended

How & Where?

gui build log

Reproducible (Yes/No)?

yes, build the gui, look at the log

Additional Information

https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#0.3

Acceptance Criteria

• We are using supported way of doing this

How to Review

• We are using supported way of doing this