Update Erlang strings to use ~c sigil

[fhunleth]

This fixes the following warnings in Elixir 1.17:

==> gen_state_machine
Compiling 3 files (.ex)
    warning: single-quoted strings represent charlists. Use ~c"" if you indeed want a charlist or use "" instead
    │
 21 │       {'** State machine ~tp terminating~n' ++ _ = format, args} ->
    │        ~
    │
    └─ lib/gen_state_machine/translator.ex:21:8

    warning: single-quoted strings represent charlists. Use ~c"" if you indeed want a charlist or use "" instead
    │
 24 │       {'** State machine ~p terminating~n' ++ _ = format, args} ->
    │        ~
    │
    └─ lib/gen_state_machine/translator.ex:24:8