[6.x] Fix inner hits source filtering test
This PR goal was to test the new 6.8.1 version of elasticsearch/elasticsearch published yesterday by @ezimuel .
It seems it's still breaking on class Elasticsearch\Endpoints\Indices\ForceMerge which is not found anymore.
PS: It seems it's now Elasticsearch\Endpoints\Indices\Forcemerge with lowercased m 🤔
@ezimuel Don't know what to do on my side. This class renaming from Elasticsearch\Endpoints\Indices\ForceMerge to Elasticsearch\Endpoints\Indices\Forcemerge seems a bug on 6.8.1.
Recent version 7.12.0 has no issue as it uses the Elasticsearch\Endpoints\Indices\ForceMerge class naming.
Looks like ForceMerge was renamed in https://github.com/elastic/elasticsearch-php/commit/2da5f9337a269113954a84fe8e79ea6843f0e7c3#diff-c4834c4ebd492607a0af1ab55c7575c6a84323f8be87ca6f7f8833cf4ffc2675
@deguif just commented here https://github.com/elastic/elasticsearch-php/issues/1131#issuecomment-841319667
Just released elasticsearch-php 6.8.2 including the fix for this issue (https://github.com/elastic/elasticsearch-php/pull/1151).