fix erroneous code path within `show_sym` (#38830)
fix erroneous code path within `show_sym`
currently, `show_sym` can recur into `show(::IO, String)`, but it's a
bit "erroneous" since `is_syntactic_operator(::String)` is not defined.
(cherry picked from commit 6322b8c8d5a3d9666a186d9073804f14d13d22d3)
