fix(ci): correct DIST_BRANCH on release events for stream-dist deploy

[PatelUtkarsh]

Fixes the stream-dist deploy workflow failing on release events with:

error: src refspec refs/tags/v4.2.0 matches more than one
error: failed to push some refs to 'github.com:xwp/stream-dist.git'

Root cause

On a release event, GITHUB_REF is refs/tags/<tag>. The previous setup step did:

DIST_BRANCH="${GITHUB_REF#refs/heads/}"   # strip prefix that isn't there
DIST_TAG="${GITHUB_REF#refs/tags/}"

The refs/heads/ prefix strip is a no-op for tag refs, so DIST_BRANCH ended up as the literal string refs/tags/v4.2.0. The later git checkout -B "$DIST_BRANCH" then created a branch literally named refs/tags/v4.2.0 alongside the new tag of the same short name, making git push --tags origin refs/tags/v4.2.0 ambiguous (matched both the branch and the tag).

Fix

Branch on github.event_name to derive DIST_BRANCH correctly:

• On release events: pull the branch from github.event.release.target_commitish (typically master) and the tag from the ref.
• On push events: keep the previous behaviour, derive the branch from refs/heads/ and skip tagging.

Also tighten the release push to explicitly push just the target branch and the new tag instead of relying on --tags, which would push every local tag the runner happens to have.

Why this is a new failure

The release: trigger on this workflow was re-added in #1853 (2026-04-02). v4.2.0-rc.1 was the first release event to actually exercise this code path. The bug itself dates back to the September 2024 workflow rewrite and was dormant until then.

Verified failure runs

• runs/26573649458 (v4.2.0)
• runs/26493589602 (v4.2.0-rc.1)

Follow-up

The v4.2.0 tag on xwp/stream-dist is missing as a result of this failure and will need to be created manually (the dist branch itself was updated successfully by the prior push-to-master run, so only the tag is missing).

Checklist

• Project documentation has been updated to reflect the changes in this pull request, if applicable. (N/A: workflow-only fix.)
• I have tested the changes in the local development environment (see contributing.md). (N/A: cannot exercise release-event workflow locally; will validate on next release.)
• I have added phpunit tests. (N/A: workflow change.)