Ensure renovate ignores postgres subchart upstream images

Currently Renovate is monitoring the upstream (dockerhub) images for the postgres subchart. For example see this MR. The changes to chart/deps/postgresql/values.yaml are undesired.

We should ensure that all files under chart/deps are ignored. Previously the ignore paths value here was added to exclude this, but it either did not actually work or something changed in the renovate config format.