Offline gradle wrapper Setup still wants to download gradle[…]src.zip

We need to use a gradle project in an offline only environment. With setting the ‘distributionUrl’ to a local folder we can use a locally available gradle-6.8-bin.zip.

But during building the corresponding gradle-6.8-src.zip is tried to be downloaded which obviously fails.
How can we ship a local gradle-6.8-src.zip ?

Btw: this also happens when setting the distributionUrl to gradle-6.8-all.zip