fix(promtail): Fix API level node filtering of Kubernetes SD to only fetch pod metadata for pods of the current node

[LashaJini]

What this PR does / why we need it:

Previous behavior: loop variable selector is a copy of each element, thus changes to the fields is not reflected in the original slice.

Current behavior: use index of the element and update directly.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[chaudum]

Thanks! LGTM

[LashaJini]

add the missing err assertion to satisfy the linter

[LashaJini]

@chaudum could you please remove the invalid labels. I've accidentally pushed the wrong changes and gh actions bot didn't remove the invalid ones.