Bump actions/upload-artifact from 5 to 6 #628

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 3.2	26s
ubuntu-24.04 3.4	24s
ubuntu-24.04 3.1	27s
ubuntu-24.04 debug	30s
ubuntu-24.04 truffleruby-head	49s
ubuntu-24.04 3.0	21s
ubuntu-24.04 3.3	29s
ubuntu-24.04 head	25s
ubuntu-24.04 2.7	57s
ubuntu-22.04 3.4	28s
ubuntu-22.04 jruby-head	1m 25s
ubuntu-22.04 3.2	27s
ubuntu-22.04 truffleruby-head	46s
ubuntu-22.04 3.1	22s
ubuntu-22.04 3.0	32s
ubuntu-24.04 jruby-head	1m 26s
ubuntu-22.04 3.3	29s
ubuntu-22.04 debug	36s
ubuntu-22.04 2.7	51s
ubuntu-22.04 head	26s
	12m 40s

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