Incompatible changes break upgrade

Describe the issue

Currently I'm running 4.14.2 and trying to upgrade to 4.14.latest, which fails.

First error is this

$ helm upgrade -n weblate weblate weblate/weblate -f values.yaml
Error: UPGRADE FAILED: execution error at (weblate/charts/postgresql/templates/secrets.yaml:17:24): 
PASSWORDS ERROR: The secret "weblate-postgresql" does not contain the key "postgres-password"

After duplicating the old entry postgresql-passwort to postgres-password using kubectl -n weblate edit secret/weblate-postgresql I now get the next error (reformatted for readability):

$ helm upgrade -n weblate weblate weblate/weblate -f values.yaml
Error: UPGRADE FAILED:
cannot patch "weblate-postgresql" with kind StatefulSet: StatefulSet.apps "weblate-postgresql" is invalid: spec:
  Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden
&&
cannot patch "weblate-redis-master" with kind StatefulSet: StatefulSet.apps "weblate-redis-master" is invalid: spec:
  Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden

I already tried

• I've read and searched the documentation.
• I've searched for similar issues in this repository.

Steps to reproduce the behavior

1. helm upgrade -n weblate weblate weblate/weblate -f values.yaml

Expected behavior

helm upgrading Weblate

Screenshots

No response

Exception traceback

$ helm upgrade -n weblate weblate weblate/weblate -f values.yaml --debug
…
client.go:250: [debug] error updating the resource "weblate-postgresql":
         cannot patch "weblate-postgresql" with kind StatefulSet: StatefulSet.apps "weblate-postgresql" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden
client.go:510: [debug] Patch StatefulSet "weblate-redis-master" in namespace weblate
client.go:250: [debug] error updating the resource "weblate-redis-master":
         cannot patch "weblate-redis-master" with kind StatefulSet: StatefulSet.apps "weblate-redis-master" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden

$ helm upgrade -n weblate weblate weblate/weblate -f values.yaml --debug --dry-run
…

### Additional context

_No response_

Start with the Helm upgrade command and the reported failure in weblate/charts/postgresql/templates/secrets.yaml:17:24. Compare the existing PostgreSQL and Redis StatefulSet specifications with those rendered by the 4.14.latest chart, including the postgres-password secret requirement. Done means an upgrade from 4.14.2 completes without manual secret edits or forbidden StatefulSet changes.