chore: add modernizer linter (#11936)

- Go has a suite of small linters that helps with modernizing Go code by using newer functions and catching small mistakes, https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/modernize.
- Enable this linter in golangci-lint.
- There's also [`go fix`](https://go.dev/blog/gofix), which is not yet released as a linter in golangci-lint: https://github.com/golangci/golangci-lint/pull/6385

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11936
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/repository/init.go

@@ -152,7 +152,7 @@ func InitializeLabels(ctx context.Context, id int64, labelTemplate string, isOrg
 	}
 
 	labels := make([]*issues_model.Label, len(list))
-	for i := 0; i < len(list); i++ {
+	for i := range list {
 		labels[i] = &issues_model.Label{
 			Name:        list[i].Name,
 			Exclusive:   list[i].Exclusive,