Ensure target is reset before loading a jdk pipeline config file

[andrew-m-leonard]

Fixes #773

When pipeline config is loaded via a groovy "target = load ", target is set to the current groovy binding, and all the variables loaded are set in the groovy variable binding.
When a 2nd load is performed the target return is the same "current groovy binding", thus any previous version loaded variable values will still be set... hence why the jdk21 schedule was being set to the jdk17u schedule!

This PR ensures at the end of each iteration the target binding values are reset.

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[andrew-m-leonard]

run tests

[eclipse-temurin-bot]

 PR TESTER RESULT 

✅ All pipelines passed! ✅

[sxa]

I'd question whether a try/catch is the nicest way to achieve this, but if we're confident that it fixes the problem I'll give my tentative approval on it (But to be clear I'm not an expert in this area of the code)