Add changelog entry for deprecating getBlobSidecars endpoint (#560)

Author: nflaig

CHANGES.md

@@ -12,6 +12,7 @@ There are likely to be descriptions etc outside of the list below, but new query
 | [#537](https://github.com/ethereum/beacon-APIs/pull/537) `GET /eth/v1/debug/beacon/data_column_sidecars/{block_id}` added         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#539](https://github.com/ethereum/beacon-APIs/pull/539) `GET /eth/v1/beacon/states/{state_id}/proposer_lookahead` added         |                                                  |                                                  |                                                    |                                                 |                                           |
 | [#546](https://github.com/ethereum/beacon-APIs/pull/546) `GET /eth/v1/beacon/blobs/{block_id}` added         |                                                  |                                                  |                                                    |                                                 |                                           |
+| [#546](https://github.com/ethereum/beacon-APIs/pull/546) `GET /eth/v1/beacon/blob_sidecars/{block_id}` deprecated         |                                                  |                                                  |                                                    |                                                 |                                           |
 
 The Following are no longer in the Standard API, removed since the latest version.