update docker build script to pick version

.gitea/workflows/build-docker.yml

@@ -15,7 +15,7 @@ jobs:
 
       - name: Read current version
         id: get_version
-        run: echo "current_version=$(cat VERSION)" >> $GITHUB_ENV
+        run: echo "current_version=$(cat version.txt)" >> $GITHUB_ENV
 
       - name: Increment version
         id: increment_version
@@ -25,7 +25,6 @@ jobs:
           version_parts[2]=$((version_parts[2] + 1))
           new_version="${version_parts[0]}.${version_parts[1]}.${version_parts[2]}"
           echo "new_version=$new_version" >> $GITHUB_ENV
-          echo $new_version > VERSION
 
       - name: Log in to Gitea Docker Registry
         run: echo "${{ secrets.DOCKER_PASSWORD }}" | docker login https://gitea.suda.codes -u ${{ secrets.DOCKER_USERNAME }} --password-stdin