Bump actions/checkout from 5 to 6 (#4) #25

Job	Run time
Julia lts - windows-latest - x64 - push	4m 2s
Julia lts - macOS-latest - x64 - push	6m 53s
Julia 1 - windows-latest - x64 - push	6m 28s
Julia 1 - macOS-latest - x64 - push	7m 54s
Julia lts - ubuntu-latest - x64 - push	3m 6s
Julia 1 - ubuntu-latest - x64 - push	4m 2s
	32m 25s

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