Update docker/login-action digest to 81c6f93

Author: uniproject-renovate[bot]

.github/workflows/docker-tag.yaml

@@ -23,7 +23,7 @@ jobs:
         run: tagname=${GITHUB_REF#refs/*/} && echo "TAG_NAME=${tagname#v}" >> $GITHUB_ENV
 
       - name: Login to GitHub Container Registry
-        uses: docker/login-action@650006c6eb7dba73a995cc03b0b2d7f5ca915bee # v4
+        uses: docker/login-action@81c6f93d4bc991e510b342a00b419b3bb4efc5c6 # v4
         with:
           registry: registry.uniproject.jp
           username: robot$github-publisher