fix: correct async import hook that disables the code-interpreter module blocklist (#27245)

The middleware code-interpreter path defines `restricted_import` as `async def` and assigns it to `builtins.__import__`, which Python's import machinery calls synchronously. Calling an async function returns a coroutine without running its body, so the blocklist check never executes and `_real_import` is never called. When `CODE_INTERPRETER_BLOCKED_MODULES` is set, blocked modules are therefore not blocked, and every subsequent import inside the interpreter binds a dangling coroutine instead of the module, breaking legitimate imports as well.

Define the hook as a regular `def`, matching the working implementation in `tools/builtin.py`. A blocked top-level import now raises `ImportError`, and all other imports pass through to the real importer.

backend/open_webui/utils/middleware.py

@@ -5179,7 +5179,7 @@ async def streaming_chat_response_handler(response, ctx):
                                         BLOCKED_MODULES = {CODE_INTERPRETER_BLOCKED_MODULES}
     
                                         _real_import = builtins.__import__
-                                        async def restricted_import(name, globals=None, locals=None, fromlist=(), level=0):
+                                        def restricted_import(name, globals=None, locals=None, fromlist=(), level=0):
                                             if name.split('.')[0] in BLOCKED_MODULES:
                                                 importer_name = globals.get('__name__') if globals else None
                                                 if importer_name == '__main__':