Fix gemspec to include .jar files #635

Job	Run time
Ruby memcheck	1m 1s
ruby-versions / Generate Ruby versions	2s
ubuntu-22.04 2.7	54s
ubuntu-22.04 3.0	31s
ubuntu-22.04 3.1	32s
ubuntu-22.04 3.2	27s
ubuntu-22.04 3.3	34s
ubuntu-22.04 head	1m 18s
ubuntu-22.04 jruby	1m 7s
ubuntu-22.04 jruby-head	1m 7s
macos-13 2.7	1m 46s
macos-13 3.0	34s
macos-13 3.1	45s
macos-13 3.2	52s
macos-13 3.3	41s
macos-13 head	43s
macos-13 jruby	1m 35s
macos-13 jruby-head	1m 41s
macos-14 2.7	1m 16s
macos-14 3.0	24s
macos-14 3.1	38s
macos-14 3.2	20s
macos-14 3.3	38s
macos-14 head	21s
macos-14 jruby	41s
macos-14 jruby-head	38s
windows-latest 2.7	4m 5s
windows-latest 3.0	2m 13s
windows-latest 3.1	2m 19s
windows-latest 3.2	3m 3s
windows-latest 3.3	2m 24s
windows-latest head	1m 26s
windows-latest mswin	1m 4s
ubuntu-latest jruby-9.4	1m 4s
macos-latest truffleruby-head	56s
ubuntu-latest truffleruby-head	1m 55s
	41m 35s

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