* R/generation.R: Use set instead of := #709

Job	Run time
Check windows-latest (release)	15m 2s
Check windows-latest (4)	14m 51s
Check macos-13 (release)	11m 36s
Check macos-13 (4)	8m 34s
Check macos-14 (release)	5m 15s
Check macos-14 (4)	6m 34s
Check ubuntu-20.04 (4.0)	8m 10s
Check ubuntu-22.04 (release)	7m 26s
Check ubuntu-24.04 (devel)	11m 9s
Coverage	10m 32s
pkgdown	4m 28s
	1h 43m 37s

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