Fix catch-all shard failing with “Missing test product” on suite-granularity sharding

Fixes a failure of the catch-all shard when using suite-granularity sharding with split (per-module) uploads. Previously, that shard downloaded only the shared artifact because its module list was empty, but the shared xctestrun references every built test target, so xcodebuild failed with “Missing test product” for the per-module .xctest bundles. The shard now downloads every module’s test products (including targets with no suite history), so the catch-all can run the full plan minus the suites already assigned to earlier shards.