Update to rennovate and pin digest

As a Numba developer I want all the numba repos to use the same tools in highly similar configuration to increase coherence across sub-projects. As such this project needs:

* [ ] an update to use rennovate, as both [llvmlite](https://github.com/numba/llvmlite) and [numba-scfg ](https://github.com/numba/numba-scfg)projects use that
* [ ] configure rennovate to pin to digest / SHA1 sum for security hardening (like: https://github.com/numba/llvmlite/pull/1156 and https://github.com/numba/numba-scfg/pull/175)