lib/gitlab/ci/tags/bulk_insert.rb seems not slicing TAGGINGS_BATCH_SIZE

In lib/gitlab/ci/tags/bulk_insert.rb we slice TAGGINGS_BATCH_SIZE but use the whole thing. It should use taggings_slice

The following discussion from !90588 (merged) should be addressed:

• @tkuah started a discussion:

  I noticed we are slicing but using the whole array here. Seems like a bug 😄