ci: fix docker bake v7 workdir configuration via source

Author: denniseffing

.github/workflows/app-builder.yaml

@@ -137,9 +137,8 @@ jobs:
             *.output=type=image,name=ghcr.io/${{ github.repository_owner }}/${{ inputs.app }},push-by-digest=true,name-canonical=true,push=true,compression=zstd,force-compression=true
             *.platform=${{ matrix.platform }}
             *.tags=
-          source: .
+          source: ./apps/${{ inputs.app }}
           targets: image
-          workdir: ./apps/${{ inputs.app }}
 
       - name: Export Digest
         run: |-