fix: BotTokens の accessToken を nullable にする

Author: otukado

docs/v3-api.yaml

@@ -6471,6 +6471,7 @@ components:
         accessToken:
           type: string
           description: BOTアクセストークン
+          nullable: true
       required:
         - verificationToken
         - accessToken

router/v3/responses.go

@@ -210,8 +210,8 @@ func formatBots(bs []*model.Bot) []*Bot {
 }
 
 type BotTokens struct {
-	VerificationToken string `json:"verificationToken"`
-	AccessToken       string `json:"accessToken"`
+	VerificationToken string              `json:"verificationToken"`
+	AccessToken       optional.Of[string] `json:"accessToken"`
 }
 
 type BotDetail struct {