fix(abi): do not error on the nothing-to-repair path

A slot with verdicts recorded but nothing unsafe died on its own success
message:

  Error in sprintf("%s/%s: %d objects recorded, none unsafe. Nothing to repair.", ...)

RPostgres returns count(*) as integer64, which %d rejects. The pipeline step
then failed for a slot that was in the best possible state, which is the wrong
signal entirely.

local/list-unsafe-flat-objects.R

@@ -141,11 +141,13 @@ if (nrow(rows) == 0L) {
       call. = FALSE
     )
   }
+  # `count(*)` arrives as a double (or integer64), and `%d` rejects both, so the
+  # nothing-to-do path used to die on its own success message.
   message(sprintf(
-    "%s/%s: %d objects recorded, none unsafe. Nothing to repair.",
+    "%s/%s: %s objects recorded, none unsafe. Nothing to repair.",
     arch,
     codename,
-    total
+    format(as.numeric(total), scientific = FALSE)
   ))
   quit(status = 0)
 }