RFR: 8340306: Add border around instructions in PassFailJFrame

[Alexey Ivanov]

A trivial change which adds border around instruction text. It makes the text easier to read.

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Commit messages:
 - 8340306: Add border around instructions in PassFailJFrame

Changes: https://git.openjdk.org/jdk/pull/21038/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21038&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340306
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21038.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21038/head:pull/21038

PR: https://git.openjdk.org/jdk/pull/21038