cli-plugins/manager: remove redundant capturing of loop vars (copyloopvar)

go1.22 and up now produce a unique variable in loops, tehrefore no longer
requiring to capture the variable manually;

    cli-plugins/manager/cobra.go:55:4: The copy of the 'for' variable "p" can be deleted (Go 1.22+) (copyloopvar)
                p := p
                ^

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli-plugins/manager/cobra.go

@@ -52,7 +52,6 @@ func AddPluginCommandStubs(dockerCli command.Cli, rootCmd *cobra.Command) (err e
 			return
 		}
 		for _, p := range plugins {
-			p := p
 			vendor := p.Vendor
 			if vendor == "" {
 				vendor = "unknown"