[Bug #19081] Show the caller location in warning for Ractor
The internal location in ractor.rb is not usefull at all.
```
$ ruby -e 'Ractor.new {}'
<internal:ractor>:267: warning: Ractor is experimental, ...
```
---
bootstraptest/test_ractor.rb | 6 ++++++
ractor.c | 6 ------
ractor.rb | 4 ++++
3 files changed, 10 insertions(+), 6 deletions(-)