Update etc/extensions.yml on master and v9.0: add the glibc-floor variant key(s) with checksums from the publish-lanes ticket (CLOUDP-437688), pinned to the first extension version that has floor artifacts - independent of TLS state, so this never waits on the TLS implementation. Executes the replacement decision from the Scope/TDs: once the AL2023 row of the glibc-floor spike's validation passed (CLOUDP-437685), retire the amazon2023-specific keys in favor of the floor keys (one artifact per arch, one publish surface). Update resmoke's external-extension downloader in the same change, since it hardcodes the amazon2023 key names and silently skips unknown variants.

Acceptance:

• manifest carries the floor keys with checksums
• resmoke downloads the right artifact on both arches
• a decision recorded on amazon2023 key retirement

Part of CLOUDP-437684. Depends on CLOUDP-437688 (published artifacts and checksums) and SERVER-133863 (Scope/TD).