data_interfaces: DataPeerUnit adding secret is broken

[juditnovak]

Steps to reproduce

1. Try to add a unit-level secret

Expected behavior

The secret is added

Actual behavior

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-postgresql-1/charm/./src/charm.py", line 1475, in <module>
    main(PostgresqlOperatorCharm)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/main.py", line 436, in main
    _emit_charm_event(charm, dispatcher.event_name)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/main.py", line 144, in _emit_charm_event
    event_to_emit.emit(*args, **kwargs)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/framework.py", line 340, in emit
    framework._emit(event)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/framework.py", line 842, in _emit
    self._reemit(event_path)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/framework.py", line 931, in _reemit
    custom_handler(event)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/postgresql_k8s/v0/postgresql_tls.py", line 117, in _on_tls_relation_joined
    self._request_certificate(None)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/postgresql_k8s/v0/postgresql_tls.py", line 97, in _request_certificate
    self.charm.set_secret(SCOPE, "key", key.decode("utf-8"))
  File "/var/lib/juju/agents/unit-postgresql-1/charm/./src/charm.py", line 264, in set_secret
    self.peer_relation_unit.update_relation_data(peers.id, {key: value})
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 451, in wrapper
    return f(self, *args, **kwargs)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 999, in update_relation_data
    return self._update_relation_data(relation, data)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 1582, in _update_relation_data
    _, normal_fields = self._process_secret_fields(
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 800, in _process_secret_fields
    if group_result := operation(relation, group, secret_fields, *args, **kwargs):
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 1096, in _add_or_update_relation_secrets
    return self._add_relation_secret(relation, group, secret_fields, data, uri_to_databag)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 462, in wrapper
    return f(self, *args, **kwargs)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 1050, in _add_relation_secret
    secret = self.secrets.add(label, content, relation)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 571, in add
    secret.add_secret(content, relation)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/lib/charms/data_platform_libs/v0/data_interfaces.py", line 494, in add_secret
->>>>>>>>>>>>>>>>>>>>>    secret = self.charm.app.add_secret(content, label=self.label)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/model.py", line 442, in add_secret
    id = self._backend.secret_add(
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/model.py", line 3372, in secret_add
    result = self._run('secret-add', *args, return_output=True)
  File "/var/lib/juju/agents/unit-postgresql-1/charm/venv/ops/model.py", line 2948, in _run
    raise ModelError(e.stderr) from e
ops.model.ModelError: ERROR this unit is not the leader

Versions

Operating system: Ubuntu LTS

Juju CLI: 3.1.7

Juju agent: 3.1.6

Log output

Juju debug log: see above

Additional context

[github-actions[bot]]

https://warthogs.atlassian.net/browse/DPE-3250