[jdk26] RFR: 8373909: JSpec and ToolGuide taglets use incorrect relative path

[Dan Smith]

This pull request contains a backport of commit [0b271240](https://github.com/openjdk/jdk/commit/0b2712400b55d4a512db225d090c2f06f01f7f1f) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

The commit being backported was authored by Dan Smith on 18 Dec 2025 and was reviewed by Chen Liang and Hannes Wallnöfer.

-------------

Commit messages:
 - Backport 0b2712400b55d4a512db225d090c2f06f01f7f1f

Changes: https://git.openjdk.org/jdk/pull/28902/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28902&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373909
  Stats: 94 lines in 4 files changed: 28 ins; 48 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/28902.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28902/head:pull/28902

PR: https://git.openjdk.org/jdk/pull/28902