Enhance Docker build workflow with Dockerfile management

Added steps to save and restore Dockerfile during the workflow.

.github/workflows/docker-build.yml

@@ -13,6 +13,9 @@ jobs:
         with:
           submodules: recursive
 
+      - name: Save Dockerfile
+        run: cp Dockerfile /tmp/Dockerfile
+
       - name: Fetch upstream tag
         run: |
           git remote add upstream https://github.com/Lidarr/Lidarr.git
@@ -20,6 +23,9 @@ jobs:
           git checkout v3.1.0.4875
           git submodule update --init --recursive
 
+      - name: Restore Dockerfile
+        run: cp /tmp/Dockerfile ./Dockerfile
+
       - name: Apply fix
         run: |
           sed -i 's/_rootFolderService.All().Select(x => x.Path).ToList();/artists.Select(x => x.Path).ToList();/' src/NzbDrone.Core/Music/Services/RefreshArtistService.cs