In 蛍の墓 there is a scene where the mother says:

ほな、ひと足先に壕に行かしてもらうからね。

What does 行かしてもらうから mean?

I know usually もらう means to receive / get someone to do something.

I’ve never seen this conjugation of 行く before. Is it a casual form of 行かせて？ where せ—>し？

In 火垂るの墓 there is a scene where the mother says:

ほな、ひと足先に壕に行かしてもらうからね。

What does 行かしてもらうから mean?

I know usually もらう means to receive / get someone to do something.

I’ve never seen this conjugation of 行く before. Is it a casual form of 行かせて？ where せ—>し？