* Revert "Saving and restoring the go cache was an experiment to reduce build times, but it worked too inconsistently. (#10493)"
This reverts commit 1e72bb1c41aef6648e9e219f6e44ae7942f463fe.
* make ci-config
* ci: update default go image to use docker mirror
* bump to go1.15.11
- Previously there was version skew: 1.15.10 and 1.15.4 were in use.