Release: check the pom.xml version against the release tag

[tuhaihe]

The release script checked the VERSION file against the tag but never compared it with the <version> in pom.xml, which ships in the source tarball. The go-libs and pxf 2.2.0-incubating-rc2 tarballs went out with pom.xml still at 2.1.0-incubating because their scripts had the same gap; this one was right only because pom.xml had been bumped by hand.

Read the project version with xmllint, which the script already requires, and stop unless it is <base version>-incubating.

Assisted-by: Claude Code

closes: #ISSUE_Number

---

Change logs

Describe your change clearly, including what problem is being solved or what document is being added or updated.

Contributor's checklist

Here are some reminders before you submit your pull request:

• Make sure that your Pull Request has a clear title and commit message. You can take the Git commit template as a reference.
• Learn the code contribution and doc contribution guides for better collaboration.
• Make sure that CICD workflow is successful.
• List your communications in the GitHub Issues or Discussions (if has or needed).
• Feel free to ask for the cloudberry committers or other people to help review and approve.

[tuhaihe]

verified:

[gpadmin@cdw cloudberry-backup]$ ./cloudberry-backup-release.sh --stage --tag 2.2.0-incubating-rc3 -S -k --repo ~/cloudberry-backup/
INFO: GPG signing has been intentionally skipped (--skip-signing).

=================================================================
>> Platform and Tool Detection
=================================================================
Platform detected: Linux

[OK] SHA-512 tool: sha512sum
[OK] Tar tool: tar
- GPG tool: skipped (--skip-signing enabled)
[OK] XML tool: xmllint

Press Enter or type y/yes to continue, or 'n' to exit: y

=================================================================
>> Validating Version Consistency
=================================================================
Version validation strategy:
  Tag: 2.2.0-incubating-rc3
  Base version (for source files): 2.2.0
Version consistency verified
    Release Tag   : 2.2.0-incubating-rc3
    Base Version  : 2.2.0
    VERSION file  : 2.2.0
    pom.xml       : 2.2.0-incubating

Press Enter or type y/yes to continue, or 'n' to exit: y

[MisterRaindrop]

LGTM