website gha.md: write LIMA_VERSION to $GITHUB_ENV

Fixes the `cache` action which was resolving `${{ env.LIMA_VERSION }}`
to an empty string.

Signed-off-by: Sean Gilligan <sean@msgilligan.com>

Author: msgilligan

website/content/en/docs/examples/gha.md

@@ -50,6 +50,8 @@ jobs:
         gh attestation verify --owner=lima-vm "${FILE}"
         sudo tar Cxzvf /usr/local "${FILE}"
         rm -f "${FILE}"
+        # Export LIMA_VERSION For the GHA cache key
+        echo "LIMA_VERSION=${LIMA_VERSION}" >>$GITHUB_ENV
 
     - name: "Cache ~/.cache/lima"
       uses: actions/cache@v4