It's . {} does not have that reading and you won't find it in dictionaries. However, is a saying in Japanese which does have an almost identical meaning.
Why do they use []{}[]{}?
This study divides the reason into 7 forms:
①
②
③
④
⑤
⑥
⑦
I would say is a form※, i.e. you hear is used when speaking but not in writing. However, manga often depict colloquial conversations, which is why you see it's use here.
※You could also consider to be ``.
What is happening here, is by blending the spoken and written forms, you get full understanding, but also the reading portrays a real spoken conversation, so the manga doesn't feel very "stiff" like reading a long non-fiction novel.
Here is another study for people who want to read further about Ateji.