MAINT: Set requires-pixi in pixi.toml #20410

Job	Run time
detect ci trigger	7s
Event File	5s
cache-pixi-lock	2m 26s
windows-latest \| test-py311	21m 4s
ubuntu-latest \| test-py313 (flaky)	7m 42s
ubuntu-latest \| test-py311-with-typing (mypy)	3m 46s
ubuntu-latest \| test-py313	10m 51s
ubuntu-latest \| test-py311-bare-min-and-scipy	2m 45s
ubuntu-latest \| test-py313-with-typing	21m 47s
ubuntu-latest \| test-py313-no-numba	9m 55s
macos-latest \| test-py311	17m 53s
windows-latest \| test-py313	20m 51s
ubuntu-latest \| test-py311-bare-minimum	3m 2s
ubuntu-latest \| test-py311	10m 56s
ubuntu-latest \| test-py311-min-versions	9m 55s
macos-latest \| test-py313	17m 20s
ubuntu-latest \| test-py313-no-dask	11m 42s
	2h 52m 7s

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