Fix compiler warnings with Elixir v17+/18+

[agatheblues]

warning: single-quoted string represent charlists. Use ~c''' if you indeed want a charlist or use """ instead
    │
 31 │     '''
    │     ~
    │
    └─ lib/bitstyles_phoenix/alpine3/dropdown.ex:31:5

    warning: single-quoted string represent charlists. Use ~c''' if you indeed want a charlist or use """ instead
    │
 85 │     '''
    │     ~
    │
    └─ lib/bitstyles_phoenix/alpine3/dropdown.ex:85:5
...