fix: disable SponsoredFPC on staging-public

The SponsoredFPC contract address changes when aztec-nr is updated
(different bytecode → different class ID → different address), which
causes the genesis archive root to change and bricks nodes running
a different aztec-nr version.

Disabling it makes staging-public match the testnet/mainnet config,
avoiding genesis root divergence across versions.

Author: AztecBot

spartan/environments/staging-public.env

@@ -24,7 +24,7 @@ TX_COLLECTION_FILE_STORE_URLS="https://aztec-labs-snapshots.com/${TX_FILE_STORE_
 R2_ACCESS_KEY_ID=REPLACE_WITH_GCP_SECRET
 R2_SECRET_ACCESS_KEY=REPLACE_WITH_GCP_SECRET
 TEST_ACCOUNTS=false
-SPONSORED_FPC=true
+SPONSORED_FPC=false
 
 # Match testnet/mainnet mana target (75M) instead of global default (100M).
 # AZTEC_MANA_TARGET only takes effect on L1 contract redeployment.