[jdk22u] RFR: 8331331: :tier1 target explanation in doc/testing.md is incorrect [v2]

[SendaoYan]

> Hi,
>   This is clean backport of [JDK-8331331](https://bugs.openjdk.org/browse/JDK-8331331), fixed the incorrect explanation :tier1 target in doc/testing.md. No risk.

SendaoYan has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into backport-sendaoYan-04271dfe
 - Backport 04271dfe7a262379944e2a2cf83a98a3a1b78a74

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

Changes:
  - all: https://git.openjdk.org/jdk22u/pull/183/files
  - new: https://git.openjdk.org/jdk22u/pull/183/files/38fe94a0..0116306c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk22u&pr=183&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk22u&pr=183&range=00-01

  Stats: 1537 lines in 16 files changed: 346 ins; 1025 del; 166 mod
  Patch: https://git.openjdk.org/jdk22u/pull/183.diff
  Fetch: git fetch https://git.openjdk.org/jdk22u.git pull/183/head:pull/183

PR: https://git.openjdk.org/jdk22u/pull/183