docs: fix GitHub links to point to v1.x branch #4206

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	34s
checks / test (3.11, lowest-direct, ubuntu-latest)	44s
checks / test (3.13, lowest-direct, ubuntu-latest)	45s
checks / test (3.10, lowest-direct, windows-latest)	2m 10s
checks / test (3.13, lowest-direct, windows-latest)	2m 20s
checks / test (3.13, highest, windows-latest)	2m 33s
checks / test (3.10, lowest-direct, ubuntu-latest)	45s
checks / test (3.10, highest, windows-latest)	2m 16s
checks / test (3.12, highest, windows-latest)	3m 15s
checks / test (3.10, highest, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, ubuntu-latest)	51s
checks / test (3.13, highest, ubuntu-latest)	47s
checks / test (3.12, highest, ubuntu-latest)	48s
checks / test (3.11, lowest-direct, windows-latest)	2m 38s
checks / test (3.11, highest, ubuntu-latest)	48s
checks / test (3.11, highest, windows-latest)	2m 31s
checks / test (3.12, lowest-direct, windows-latest)	2m 59s
all-green	4s
	27m 47s

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