ethereum: replace beaconstate.ethstaker.cc with sync-mainnet.beaconcha.in for mainnet checkpoint-sync

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

ethereum/reth/ethereum-mainnet-reth-pruned-trace.yml

@@ -119,7 +119,7 @@ services:
     command:
       - --accept-terms-of-use
       - --beacon-db-pruning
-      - --checkpoint-sync-url=https://beaconstate.ethstaker.cc
+      - --checkpoint-sync-url=https://sync-mainnet.beaconcha.in
       - --datadir=/data
       - --enable-historical-state-representation=false
       - --execution-endpoint=http://ethereum-mainnet-reth-pruned:8551