Correctly interpolate seasons in Grouper #8580

Job	Run time
Lint	1m 9s
Python3.10 (ubuntu-latest)	5m 54s
Python3.10 (ubuntu-latest, conda)	7m 2s
Python3.10 (ubuntu-latest, standard)	5m 59s
Python3.11 (ubuntu-latest, standard)	6m 0s
Python3.12 (ubuntu-latest, standard)	6m 5s
Python3.12 (ubuntu-latest, conda)	7m 27s
Python3.10 (windows-latest, py310-coverage-prefetch)	8m 35s
Python3.11 (macos-latest, py311-coverage-extras)	5m 17s
Python3.11 (ubuntu-latest, py311-coverage-sbck-offline-prefetch)	6m 21s
Python3.10 (ubuntu-latest, notebooks)	8m 22s
Python3.12 (ubuntu-latest, doctests)	3m 27s
Finish	10s
	1h 11m 48s

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