RFR: 8346285: Update jarsigner compatibility test for change in default digest algorithm

[Matthew Donovan]

In this small PR, I updated the jarsigner compatibility test to handle the difference in default digest algorithms between JDK versions. The previous default was SHA-256 but has been updated to SHA-384.

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Commit messages:
 - 8346285: Update jarsigner compatibility test for change in default digest algorithm

Changes: https://git.openjdk.org/jdk/pull/22765/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22765&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346285
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22765.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22765/head:pull/22765

PR: https://git.openjdk.org/jdk/pull/22765