[release] Fix Maven staging upload from reactor root

[XiaoHongbo-Hope]

The Maven release staging script can silently upload nothing when it is run from Paimon's multi-module repository root. The Nexus staging plugin defers a direct CLI invocation to the last reactor project, but that project is skipped in this invocation, so Maven reports BUILD SUCCESS without connecting to Nexus or creating a staging repository.

Add Maven's -N option so the root project is the only reactor project and deploy-staged-repository executes exactly once. All existing command overrides and staging safety settings remain unchanged.

The regression test uses fake Maven and GPG executables. It verifies one non-recursive staging invocation, the configurable arguments, and the existing close/release/failure behavior without contacting Nexus, uploading artifacts, or signing files.

Validation:

• python3.11 -m unittest tools.ci.test_deploy_maven_repository
• python3.11 -m unittest discover -s tools/ci -p 'test_*.py'
• bash -n tools/releasing/deploy_maven_repository.sh
• git diff --check

[JingsongLi]

Requirement fit: SUPPORTED (triage: GO)\nImplementation: CLEAN\n\nThis prevents a dangerous release false success where the staging script reports success but uploads nothing. The non-recursive Maven invocation executes the Nexus goal once at the reactor root, and the fake Maven/GPG tests retain close, release, override, and failure behavior without external side effects. No actionable P0/P1/P2 issue found.