shorten delete_splits_marked_for_deletion log

[trinity-1686a]

Description

make delete_splits_marked_for_deletion shorter. Before it used to show only a single index id, but with gc batching, it can now show thousands at once when that function returns an error.

[github-actions]

On SSD:

Average search latency is 0.991x that of the reference (lower is better).
Ref run id: 3290, ref commit: 6768d01
Link

On GCS:

Average search latency is 0.972x that of the reference (lower is better).
Ref run id: 3291, ref commit: 6768d01
Link