Kibana version: main branch, at the time of opening this issue corresponds to 8.7.0; I wasn't able to reproduce this bug in the 8.6 branch

Summary

If I start a local Package Registry and point my local Kibana to it, some of the Fleet API requests fail with 502 Error connecting to package registry.

[2023-01-19T15:13:06.488+01:00][ERROR][plugins.fleet] Error connecting to package registry: request to https://localhost:8080/search?prerelease=true&kibana.version=8.7.0 failed, reason: connect ECONNREFUSED ::1:8080
[2023-01-19T15:13:06.646+01:00][ERROR][plugins.fleet] Error connecting to package registry: request to https://localhost:8080/search?kibana.version=8.7.0 failed, reason: connect ECONNREFUSED ::1:8080
[2023-01-19T15:13:06.647+01:00][ERROR][plugins.fleet] Error connecting to package registry: request to https://localhost:8080/categories?include_policy_templates=true&kibana.version=8.7.0 failed, reason: connect ECONNREFUSED ::1:8080

Steps:

1. From the elastic/package-storage repository root, start a copy of the package registry: elastic-package stack up --services package-registry
2. Point local Kibana to the local package registry by adding the following line to kibana.dev.yml: xpack.fleet.registryUrl: https://localhost:8080
3. Start local Elasticsearch
4. Start local Kibana specifying extra certificate (without it you'll get an error about self-signed certificate): NODE_EXTRA_CA_CERTS=~/.elastic-package/profiles/default/certs/ca-cert.pem yarn start
5. Visit http://localhost:5601/kbn/app/integrations/browse