Fix/val_sample_weight error for models inherited from RegressionModel #5368

Job	Run time
lint	25s
tests (macos-13, 3.10, all)	38m 59s
check-examples (03-FFT-examples.ipynb)	3m 3s
tests (ubuntu-latest, 3.10, all)	29m 54s
docs	7m 26s
check-examples (04-RNN-examples.ipynb)	7m 42s
check-examples (00-quickstart.ipynb)	8m 10s
check-examples (02-data-processing.ipynb)	3m 36s
check-examples (01-multi-time-series-and-covariates.ipynb)	7m 7s
	1h 46m 22s

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