fix: loop variable capture and linter (#7328)

Enable copyloopvar linter and remove redundant variable
shadowing in Kubernetes plugin metadata handling. This pattern is
no longer needed in Go 1.22+ where loop variables are automatically
captured correctly in closures.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

.golangci.yml

@@ -2,13 +2,14 @@ version: "2"
 linters:
   default: none
   enable:
+    - copyloopvar
     - govet
     - ineffassign
     - staticcheck
     - unconvert
     - unused
-    - whitespace
     - usetesting
+    - whitespace
   exclusions:
     generated: lax
     presets:

plugin/kubernetes/metadata.go

@@ -21,7 +21,6 @@ func (k *Kubernetes) Metadata(ctx context.Context, state request.Request) contex
 		})
 
 		for k, v := range pod.Labels {
-			v := v
 			metadata.SetValueFunc(ctx, "kubernetes/client-label/"+k, func() string {
 				return v
 			})