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/issue/template/template.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"net/url"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -447,12 +448,7 @@ func (o *valuedOption) IsChecked() bool {
 	case api.IssueFormFieldTypeDropdown:
 		checks := strings.Split(o.field.Get(fmt.Sprintf("form-field-%s", o.field.ID)), ",")
 		idx := strconv.Itoa(o.index)
-		for _, v := range checks {
-			if v == idx {
-				return true
-			}
-		}
-		return false
+		return slices.Contains(checks, idx)
 	case api.IssueFormFieldTypeCheckboxes:
 		return o.field.Get(fmt.Sprintf("form-field-%s-%d", o.field.ID, o.index)) == "on"
 	}