Reuse installed ginkgo and use cleaner binary check

[jorbaum]

Description

Adjusts test scripts just like cloudfoundry/loggregator-agent-release#717 :

• reuse ginkgo instead of recompiling every time, same as we are already doing with golangci-lint
• cleaner check for binary removing three lines of code ;)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Testing performed?

• Unit tests
• Integration tests
• Acceptance tests

Checklist:

• This PR is being made against the main branch, or relevant version branch
• I have made corresponding changes to the documentation
• I have added testing for my changes