RFR: build: update to JUnit 5.8.2

[Christian Stein]

This patch that updates JUnit Jupiter to 5.8.2 and JUnit Platform to 1.8.2.

PS: The text at https://github.com/openjdk/skara#testing reading "_JUnit 5.6.2 or later is required to run the unit tests._" seems to be out of date. Shouldn't it read like: "A recent version of JUnit 5 is..."?

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Commit messages:
 - build: update to JUnit 5.8.2

Changes: https://git.openjdk.java.net/skara/pull/1260/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1260&range=00
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/1260.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1260/head:pull/1260

PR: https://git.openjdk.java.net/skara/pull/1260