ci: add v1.x branch to main-checks workflow #3909

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	31s
checks / test (3.10, highest, windows-latest)	2m 38s
checks / test (3.11, highest, windows-latest)	2m 31s
checks / test (3.11, highest, ubuntu-latest)	44s
checks / test (3.10, lowest-direct, windows-latest)	2m 21s
checks / test (3.10, lowest-direct, ubuntu-latest)	44s
checks / test (3.10, highest, ubuntu-latest)	49s
checks / test (3.11, lowest-direct, ubuntu-latest)	45s
checks / test (3.13, lowest-direct, ubuntu-latest)	46s
checks / test (3.11, lowest-direct, windows-latest)	3m 12s
checks / test (3.12, lowest-direct, windows-latest)	4m 0s
checks / test (3.13, highest, windows-latest)	2m 28s
checks / test (3.12, highest, windows-latest)	3m 24s
checks / test (3.12, highest, ubuntu-latest)	53s
checks / test (3.13, lowest-direct, windows-latest)	2m 30s
checks / test (3.13, highest, ubuntu-latest)	45s
checks / test (3.12, lowest-direct, ubuntu-latest)	52s
	30m 4s

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