RFR: 8371094: --mac-signing-key-user-name "CMR Technologies Limited" no longer works

[Alexey Semenyuk]

- Fix the typo where the argument for the `String.startsWith()` function is swapped with the target string.
- Add a test.

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Commit messages:
 - 8371094: --mac-signing-key-user-name "CMR Technologies Limited" no longer works

Changes: https://git.openjdk.org/jdk/pull/28120/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28120&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371094
  Stats: 13 lines in 3 files changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28120.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28120/head:pull/28120

PR: https://git.openjdk.org/jdk/pull/28120