It's a spelling mistake. That's all.

Just a printing error

You could say it is an attempt to write in a vernacular accent; however, Ann Frank is not a writer I'm familiar with.

It's possible that this edition of the book was prepared by scanning an old edition and doing OCR (optical character recognition) on a computer. If the old edition was printed with a font where "g" and "a" are quite similar, and the program wasn't properly trained, the computer might confuse those two letters. And apparently they didn't do proper proofreading. (By the way, Anne Frank wrote originally in Dutch, so it's quite unlikely she did something like this with English words on purpose.)

no