add checksum for RISC-V version to Java 21.0.2 easyconfig

[bedroge]

This version supports RISC-V, see https://github.com/adoptium/temurin21-binaries/releases/tag/jdk-21.0.2%2B13.

Requires easybuilders/easybuild-easyblocks#3323.

[bedroge]

Test report by @bedroge
Using easyblocks from PR(s) easybuilders/easybuild-easyblocks#3323
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in total)
starfive - Linux Debian GNU/Linux 2.15, RISC-V-64, UNKNOWN, Python 3.10.9
See https://gist.github.com/bedroge/c7164691127a5e35afc2f9fe210bf945 for a full test report.

[SebastianAchilles]

Test report by @SebastianAchilles
Using easyblocks from PR(s) easybuilders/easybuild-easyblocks#3323
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in total)
arriesgado-2 - Linux Ubuntu 22.04, RISC-V-64, UNKNOWN (u74mc), Python 3.10.12
See https://gist.github.com/SebastianAchilles/7b1186e1210beed5ecbe92c057033682 for a full test report.

[SebastianAchilles]

lgtm

[SebastianAchilles]

Going in, thanks @bedroge!