upstream: fix: use errors.Is for sentinel error checks in usergroup controller (goharbor/harbor#23636)

Replace direct error equality comparisons (==) with errors.Is() in the
usergroup controller. This ensures correct behavior when sentinel errors
are wrapped, following Go best practices introduced in Go 1.13.

The errors package from Harbor's lib/errors already re-exports
errors.Is, so no additional imports are needed.

Changes:
- err == ldap.ErrNotFound  -> errors.Is(err, ldap.ErrNotFound)
- err == ldap.ErrDNSyntax  -> errors.Is(err, ldap.ErrDNSyntax)
- err != nil && err == usergroup.ErrDupUserGroup -> errors.Is(err, usergroup.ErrDupUserGroup)

Signed-off-by: Norway-02 <anshulkhetade02@gmail.com>
Co-authored-by: Wang Yan <wangyan_0219@hotmail.com>

(cherry picked from commit 2020f8d)

Upstream-Commit: 2020f8d
Upstream-PR: goharbor/harbor#23636
Upstream-Author: @Norway-02
Cherry-Pick-Status: clean
Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
(cherry picked from commit ef9e319)
Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

src/controller/usergroup/controller.go

@@ -91,18 +91,18 @@ func (c *controller) Update(ctx context.Context, id int, groupName string) error
 func (c *controller) Create(ctx context.Context, group model.UserGroup) (int, error) {
 	if group.GroupType == common.LDAPGroupType {
 		ldapGroup, err := auth.SearchGroup(ctx, group.LdapGroupDN)
-		if err == ldap.ErrNotFound || ldapGroup == nil {
+		if errors.Is(err, ldap.ErrNotFound) || ldapGroup == nil {
 			return 0, errors.BadRequestError(nil).WithMessagef("LDAP Group DN is not found: DN:%v", group.LdapGroupDN)
 		}
-		if err == ldap.ErrDNSyntax {
+		if errors.Is(err, ldap.ErrDNSyntax) {
 			return 0, errors.BadRequestError(nil).WithMessagef("invalid DN syntax. DN: %v", group.LdapGroupDN)
 		}
 		if err != nil {
 			return 0, err
 		}
 	}
 	id, err := c.mgr.Create(ctx, group)
-	if err != nil && err == usergroup.ErrDupUserGroup {
+	if errors.Is(err, usergroup.ErrDupUserGroup) {
 		return 0, errors.ConflictError(nil).
 			WithMessagef("duplicate user group, group name:%v, group type: %v, ldap group DN: %v",
 				group.GroupName, group.GroupType, group.LdapGroupDN)