[DOC] Fix double-word typos in comments

Found via `grep` for repeated words.

* set.c: Fix "or or"
* include/ruby/internal/symbol.h: Fix "is is"
* include/ruby/internal/ctype.h: Fix "in in"

v3.4.8

strnlen is not used now

bump teeny

v3.4.7

v3.4.6

bump teeny

bump teeny

v3.4.5

v3.4.4