Fix release pipeline: check remote for existing tag before pushing

[Copilot]

Summary

The release pipeline was failing with:

! [rejected]        v0.15.29 -> v0.15.29 (already exists)
error: failed to push some refs to 'https://github.com/JerrettDavis/JD.Efcpt.Build'
hint: Updates were rejected because the tag already exists in the remote.

Root Cause

The "Create and push git tag" step used git rev-parse "v${PACKAGE_VERSION}" to check if a tag already existed — but this only checks local refs. If a previous run had already pushed the tag to the remote, but the current run's local repo didn't have that tag fetched, the check would pass and the push would be attempted, only to be rejected by the remote.

Fix

Replaced git rev-parse with git ls-remote --exit-code --tags origin "refs/tags/v${PACKAGE_VERSION}", which queries the remote directly. This correctly detects an already-existing remote tag and skips the push.