fix: 修复提供商源修改 ID 后保存被静默还原的问题 (#8915)

* Update schemas.py

* Update schemas.py

astrbot/dashboard/schemas.py

@@ -418,10 +418,10 @@ class ProviderSourceRequest(OpenModel):
             self.config
             or self.model_dump(exclude={"source_id", "config"}, exclude_none=True)
         )
-        if fallback_id:
-            config["id"] = fallback_id
-        elif self.id and "id" not in config:
-            config["id"] = self.id
+        if not config.get("id"):
+            # 不覆盖已有 id；self.id（显式指定）优先于 fallback_id（旧值兜底）
+            if fallback := (self.id or fallback_id):
+                config["id"] = fallback
         return config