use ~/.config/dagger rather than ~/.dagger

since `.dagger` directories have a special meaning now because of gitflow,
it's better not to have a `~/.dagger` since it's not a workspace and
it confuses dagger (e.g. `dagger new` from $HOME).

We don't store state there anymore, just keys and the last version
check, so it's okay to be in ~/.config IMO

Looking at my system, in ~/.config there's `gcloud`, `gatsby`, `gh`,
`yarn`, and others so it seems like a pretty common location.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

.github/workflows/ci.yml

@@ -86,8 +86,8 @@ jobs:
         env:
           DAGGER_AGE_KEY: ${{ secrets.DAGGER_AGE_KEY }}
         run: |
-          mkdir ~/.dagger
-          echo "$DAGGER_AGE_KEY" > ~/.dagger/keys.txt
+          mkdir -p ~/.config/dagger
+          echo "$DAGGER_AGE_KEY" > ~/.config/dagger/keys.txt
 
       - name: Login to Docker Hub
         uses: docker/login-action@v1