Bump julia-actions/cache from 1 to 2 #267

Job	Run time
Julia 1.6 - ubuntu-latest - x64	12m 8s
Julia 1.6 - ubuntu-latest - x86	14m 12s
Julia 1.6 - macOS-latest - x64	12m 20s
Julia 1.6 - windows-latest - x64	18m 1s
Julia 1.6 - windows-latest - x86	28m 50s
Julia 1 - ubuntu-latest - x64	10m 25s
Julia 1 - ubuntu-latest - x86	13m 31s
Julia 1 - macOS-latest - x64	9m 27s
Julia 1 - windows-latest - x64	10m 45s
Julia 1 - windows-latest - x86	17m 10s
Julia nightly - ubuntu-latest - x64	13m 26s
Julia nightly - macOS-latest - x64	12m 46s
Julia nightly - windows-latest - x64	14m 19s
	3h 7m 20s

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