[QA] misleading plural s in the name of new config variable `connectors_search`

[jnweiger]

Seen with search-elastic-230+refactor-connector branch 20230714

With this branch, we introduce two new variables:

occ config:app:set search_elastic connectors_write --value "Legacy,RelevanceV2"
occ config:app:set search_elastic connectors_search --value "Legacy"

While the first one holds a single value or a comma-seperated list, the second variable only holds one value.

Expected behaviour:

• The variable should be named connector_search instead of connectors_search