RFR: Clarified language around release notes

[Jesper Wilhelmsson]

The word "note" was used to refer to a release note, a release note sub-task, and a comment in a JBS issue - this could be confusing. Made it more explicit.
Also updated the usage of Fix version for release notes which was not described correctly.

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Commit messages:
 - Clarified language around release notes

Changes: https://git.openjdk.org/guide/pull/164/files
  Webrev: https://webrevs.openjdk.org/?repo=guide&pr=164&range=00
  Stats: 10 lines in 2 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/guide/pull/164.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/164/head:pull/164

PR: https://git.openjdk.org/guide/pull/164