attestation: improve debug message.

Let's reference a bottle filename here rather than a class instance ID.

Author: MikeMcQuaid

Library/Homebrew/attestation.rb

@@ -222,7 +222,7 @@ def self.check_core_attestation(bottle)
         attestation = check_attestation bottle, HOMEBREW_CORE_REPO
         return attestation
       rescue MissingAttestationError
-        odebug "falling back on backfilled attestation for #{bottle}"
+        odebug "falling back on backfilled attestation for #{bottle.filename}"
 
         # Our backfilled attestation is a little unique: the subject is not just the bottle
         # filename, but also has the bottle's hosted URL hash prepended to it.