Remove sponsor link as it was already disabled #967

Job	Run time
linters (3.9, ubuntu-latest)	50s
Testing on Python 3.8 (ubuntu-latest)	54s
Testing on Python 3.8 (macos-13)	1m 33s
Testing on Python 3.8 (windows-2019)	2m 13s
Testing on Python 3.9 (ubuntu-latest)	51s
Testing on Python 3.9 (macos-13)	1m 26s
Testing on Python 3.9 (windows-2019)	2m 52s
Testing on Python 3.10 (ubuntu-latest)	57s
Testing on Python 3.10 (macos-13)	1m 25s
Testing on Python 3.10 (windows-2019)	2m 48s
Testing on Python 3.11 (ubuntu-latest)	52s
Testing on Python 3.11 (macos-13)	1m 18s
Testing on Python 3.11 (windows-2019)	2m 54s
	20m 53s

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