GEC-136 Disable IDG unit tests when IDG is not available

Maik Nijhuisrequested to merge
gec-136-no-idg-unit-tests into master

After installing DP3 on AWS, I noticed some IDG tests run even if DP3 was compiled without IDG support.

This MR disables IDG unit tests when DP3 was compiled without IDG support.

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