[jdk21u] RFR: 8317374: Add Let's Encrypt ISRG Root X2

[Rajan Halade]

Clean backport to JDK 21u

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Commit messages:
 - Backport e6f46a43268808d0cbbb3bb93c73aa8e4cbfad83

Changes: https://git.openjdk.org/jdk21u/pull/321/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=321&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317374
  Stats: 39 lines in 3 files changed: 35 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u/pull/321.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/321/head:pull/321

PR: https://git.openjdk.org/jdk21u/pull/321