springboot Use Supplier variants of Assert

Hi,

this PR changes some Assert calls to make use of their Supplier variants in order to save the overhead of String construction in case the assertion passes.

Cheers, Christoph

Comment From: dreis2211

Couldn't create volume on CI. Do we have any indication of what this might be? It's happening relatively often these days 😞

Comment From: snicoll

Sorry about that @dreis2211. We're investigating that problem for quite some time now. There's been some progress lately.