docs: fix GitHub links to point to v1.x branch #4205

Job	Run time
checks / pre-commit	19s
checks / readme-snippets	12s
checks / test (3.12, highest, windows-latest)	3m 30s
checks / test (3.10, lowest-direct, windows-latest)	2m 16s
checks / test (3.11, lowest-direct, windows-latest)	2m 30s
checks / test (3.12, highest, ubuntu-latest)	51s
checks / test (3.10, highest, windows-latest)	2m 30s
checks / test (3.12, lowest-direct, ubuntu-latest)	59s
checks / test (3.11, lowest-direct, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, ubuntu-latest)	43s
checks / test (3.12, lowest-direct, windows-latest)	3m 20s
checks / test (3.13, lowest-direct, windows-latest)	2m 52s
checks / test (3.13, highest, windows-latest)	2m 32s
checks / test (3.13, lowest-direct, ubuntu-latest)	48s
checks / test (3.11, highest, windows-latest)	2m 29s
checks / test (3.13, highest, ubuntu-latest)	44s
checks / test (3.11, highest, ubuntu-latest)	43s
checks / test (3.10, highest, ubuntu-latest)	44s
all-green	3s
	28m 56s

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