ZJIT: Avoid mutating string in zjit stats (ruby#14485)

[ZJIT] Avoid mutating string in zjit stats

GitHub runs with a Symbol patch that causes a frozen string error when
running `--zjit-stats`

```rb
Class Symbol
  alias_method :to_s, :name
end
```

I remember hearing that Shopify runs a similar patch, and that we might
try to make this the default behavior in Ruby some day.

Any chance we can avoid mutating the string here in case it's frozen?
That does mean we'll end up making some extra strings when it's not
frozen, but I think that's OK for printing stats.

Author: composerinteralia

zjit.rb

@@ -101,7 +101,7 @@ def print_counters_with_prefix(buf:, stats:, prefix:, prompt:, limit: nil)
     counters = stats.select { |key, value| key.start_with?(prefix) && value > 0 }
     return if stats.empty?
 
-    counters.transform_keys! { |key| key.to_s.delete_prefix!(prefix) }
+    counters.transform_keys! { |key| key.to_s.delete_prefix(prefix) }
     left_pad = counters.keys.map(&:size).max
     right_pad = counters.values.map { |value| number_with_delimiter(value).size }.max
     total = counters.values.sum