RFR: 8323170 - j2dbench is using outdated javac source/target to be able to build by itself

[Jiří Vaněk]

This PR is fixig to-old values of javac source/target for jdk22.
Note, that jdk21 suffers the same, only the target values have to be 8. I will be happy to backport this cange to jdk17 later.

Note, that considering the rolling release of jdk and the reached threshold of bytecode compatibility, we will be forced to do this bump every STS, so best would be to drop this hardcoded limitation. As it obtains a bit more coding, I had filled the [JDK-8323169](https://bugs.openjdk.org/browse/JDK-8323169) - [ j2dbench need constant updating of javac source/target ](https://bugs.openjdk.org/browse/JDK-8323169)  and will be happy to fit it for jdk asap once this direct fix bubbles to jdk21

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Commit messages:
 - 8323170 - j2dbench is using outdated javac source/target to be able to build by itself

Changes: https://git.openjdk.org/jdk/pull/17303/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17303&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323170
  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/17303.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17303/head:pull/17303

PR: https://git.openjdk.org/jdk/pull/17303