Fix incompatibility of tfds.Builder.as_data_source with MultiSplitInfo. #11507

Job	Run time
Check whether we should run tests or not	11s
HuggingFace Python 3.10 tests	2m 12s
Notebook tests	6m 7s
Github API tests	2m 19s
Core TFDS tests / Generate shards	3s
Core TFDS tests / [Python 3.10][1/4]	5m 39s
Core TFDS tests / [Python 3.11][1/4]	6m 44s
Core TFDS tests / [Python 3.12][2/4]	6m 48s
Core TFDS tests / [Python 3.12][3/4]	8m 55s
Core TFDS tests / [Python 3.11][2/4]	4m 40s
Core TFDS tests / [Python 3.11][3/4]	7m 53s
Core TFDS tests / [Python 3.10][4/4]	5m 22s
Core TFDS tests / [Python 3.12][1/4]	7m 28s
Core TFDS tests / [Python 3.12][4/4]	6m 2s
Core TFDS tests / [Python 3.10][2/4]	5m 16s
Core TFDS tests / [Python 3.11][4/4]	5m 8s
Core TFDS tests / [Python 3.10][3/4]	7m 54s
	1h 28m 41s

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