[3.13] gh-125268: Use static string for "1e309" in AST (GH-125272)

[colesbury]

When formatting the AST as a string, infinite values are replaced by 1e309, which evaluates to infinity. The initialization of this string replacement was not thread-safe in the free threading build. (cherry picked from commit 427dcf2)

• Issue: Fix thread-safety of interpreter cached object str_replace_inf (free threading) #125268

[Yhg1s]

You'll have to update the ABI dump but the changes are good to go into 3.13.