ci: derive release commit from GITHUB_SHA (container lacks git)

Author: mirkobrombin

.github/workflows/release.yml

@@ -47,7 +47,7 @@ jobs:
         run: |
           mkdir -p dist
           VERSION="${GITHUB_REF_NAME}"
-          COMMIT="$(git rev-parse --short HEAD)"
+          COMMIT="${GITHUB_SHA:0:7}"
           DATE="$(date -u +%Y-%m-%dT%H:%M:%SZ)"
           LDFLAGS="-s -w -X github.com/mirkobrombin/goup/internal/cli.Version=${VERSION} -X github.com/mirkobrombin/goup/internal/cli.Commit=${COMMIT} -X github.com/mirkobrombin/goup/internal/cli.Date=${DATE}"
           OUT="dist/goup-${{ matrix.goos }}-${{ matrix.goarch }}${{ matrix.ext }}"