RFR: 8346285: Update jarsigner compatibility test for change in default digest algorithm [v2]

[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.

Matthew Donovan has updated the pull request incrementally with one additional commit since the last revision:

  updated to use JarSigner.Builder.getDefaultDigestAlgorithm()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22765/files
  - new: https://git.openjdk.org/jdk/pull/22765/files/6e080784..7d6bf2fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22765&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22765&range=00-01

  Stats: 7 lines in 1 file changed: 5 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