Adjust BWC version on bad allocation request test
This commit adjusts the BWC version on the bad cluster allocation
explain request test as changing the API to respond with a bad request
status instead of an internal server error status was backported to 5.x
to be included in 5.6.0.
Relates
"bad cluster shard allocation explanation request":
- skip:
- version: " - 5.99.99"
+ version: " - 5.5.99"
reason: response status on bad request was changed starting in 5.6.0
- do:
