[lworld] RFR: 8366802: [lworld] jdk/javadoc/doccheck/checks/jdkCheckLinks.java fails since jdk-26+26

[Chen Liang]

The missing link points to the preview note on `Attributes::loadableDescriptors`. Simply marking this API as preview fixes it.

Also I fixed the since version from 23 to Valhalla.

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Commit messages:
 - 8366802: [lworld] jdk/javadoc/doccheck/checks/jdkCheckLinks.java fails since jdk-26+26

Changes: https://git.openjdk.org/valhalla/pull/1542/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1542&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366802
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1542.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1542/head:pull/1542

PR: https://git.openjdk.org/valhalla/pull/1542