fix Missing 404 swagger response docs for /admin/users/{username} (#26086) (#26089)

Backport #26086 by @CaiCandong

close #26079

Co-authored-by: caicandong <50507092+CaiCandong@users.noreply.github.com>

routers/api/v1/admin/user.go

@@ -312,6 +312,8 @@ func DeleteUser(ctx *context.APIContext) {
 	//     "$ref": "#/responses/empty"
 	//   "403":
 	//     "$ref": "#/responses/forbidden"
+	//   "404":
+	//     "$ref": "#/responses/notFound"
 	//   "422":
 	//     "$ref": "#/responses/validationError"
 

templates/swagger/v1_json.tmpl

@@ -620,6 +620,9 @@
           "403": {
             "$ref": "#/responses/forbidden"
           },
+          "404": {
+            "$ref": "#/responses/notFound"
+          },
           "422": {
             "$ref": "#/responses/validationError"
           }