ci: only checkout docs repo when on master (#310) #1124

Job	Run time
test (ubuntu-latest, 26.3, false)	53s
test (ubuntu-latest, 28.2, false)	52s
test (macos-latest, 28.2, false)	1m 28s
test (windows-latest, 26.3, false)	2m 28s
test (ubuntu-latest, 30.1, false)	59s
test (windows-latest, 27.2, false)	1m 37s
test (ubuntu-latest, 29.4, false)	1m 2s
test (macos-latest, 30.1, false)	1s
test (windows-latest, 28.2, false)	1m 47s
test (ubuntu-latest, 27.2, false)	46s
test (ubuntu-latest, snapshot, true)	47s
test (windows-latest, 30.1, false)	1s
test (windows-latest, 29.4, false)	1s
test (macos-latest, 29.4, false)	1s
test (windows-latest, snapshot, true)	1s
test (macos-latest, snapshot, true)	1s
	12m 45s

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