helmfile added a inherit field to deal with some issues with YAML anchor "inheritance" used until now.

Implementation details at:
https://github.com/helmfile/helmfile/pull/606

Also ctrl+f for inherit at https://helmfile.readthedocs.io/en/latest/writing-helmfile/#release-template-conventional-directory-structure

helmfile 0.171.0 currently fails to validate some (not sure why not all) of our helmfiles with default settings. To prevent having to update all helmfiles right now, I've patched helmfile to move to the YAML library helmfile 1.x will use (https://gerrit.wikimedia.org/r/c/operations/debs/helmfile/+/1124151) which prevents the issues we're seeing with our helmfiles.
The patch can probably be removed when this is fixed.