Non-leader unit charm errors out on tracing-relation-xx event when integrated with Tempo over tracing

[michaeldmitry]

Bug Description

Occasionally, in CI, When a charm X is deployed with multiple units and integrated with Tempo over tracing, the non-leader unit(s) could error out during tracing-relation-xx event, as its trying to access the charm's app databag to get the receivers requested.

This probably happens due to this line when Tempo hasn't yet published the endpoints requested by the requirer charm X, but the charm X is trying to get the endpoint and when it doesn't find them in Tempo's app databag, it tries to load its own app databag to check the receivers it has requested.

To Reproduce

Deploy a multi-unit charm and integrate it with Tempo over tracing.
It occasionally happens.

Environment

microk8s: MicroK8s v1.28.13 revision 7206
juju: 3.4.5-genericlinux-amd64

Relevant log output

Check additional context

Additional context