ci: pin GoReleaser to the triggering tag, fix tag-collision regression

When v0.3.1 was tagged on the same commit as v0.3.1-rc2, the release
workflow built and tried to publish rc2 artifacts instead of v0.3.1,
failing with 'already_exists' on every asset upload.

Root cause: goreleaser-action@v6 + 'version: latest' (locked to v2.x)
falls back to 'git describe --tags' for the current tag, which picked
v0.3.1-rc2 over v0.3.1 when both refs pointed at HEAD. Explicitly
setting GORELEASER_CURRENT_TAG = github.ref_name forces the workflow
to use the tag that triggered it, regardless of other refs at the same
commit.

.github/workflows/release.yml

@@ -61,3 +61,8 @@ jobs:
           args: release --clean
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # Force GoReleaser to use the triggering tag rather than fall
+          # back to `git describe` — which can resolve to an older tag
+          # (e.g., a vX.Y.Z-rc tag) when multiple tags point at the same
+          # commit. Surfaced as the v0.3.1 release failure on 2026-05-24.
+          GORELEASER_CURRENT_TAG: ${{ github.ref_name }}