Limit retry_limit test to oniguruma >= 6.9.3

Limit retry_limit test to oniguruma >= 6.9.3

This test is somewhat fragile in that it depends on how well a
particular regex is optimized. Apparently on 6.9.1 this regex
would hit the default retry_limit of 1000000 already. I'm limiting
this to 6.9.3 because that's the version that works for me.