[jdk21u-dev] RFR: 8350260: Improve HTML instruction formatting in PassFailJFrame

[Goetz Lindenmaier]

I backport this for parity with 21.0.8-oracle.

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Commit messages:
 - Backport 014701a09b23d21f57edb5b085820532804475bd

Changes: https://git.openjdk.org/jdk21u-dev/pull/1520/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1520&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350260
  Stats: 7 lines in 1 file changed: 2 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1520.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1520/head:pull/1520

PR: https://git.openjdk.org/jdk21u-dev/pull/1520