Describe the bug
#16062 seems to have introduced a bug where the global.podLabels accumulates labels after merges are done for each component. In our environment currently only the ruler applies a label to inject istio to the pod and starting in 6.27.0 multiple workloads get that label.

I tested this by also adding a label to ingester and confirmed most (seems to me that "quer*" workloads did not receive my test label but did have the istio one from ruler) now had the istio label and my test label.

To Reproduce
Steps to reproduce the behavior:

1. Add a label to Values.ruler.podLabels
2. Templating out should show that the label is applied on multiple components

Expected behavior
Individual component labels are isolated to that component

Environment:

• Infrastructure: kubernetes
• Deployment tool: helm

Screenshots, Promtail config, or terminal output
N/A