Don't use base64 encoded key with actions/checkout.

Author: fredrikekre

.github/workflows/pkg-update.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
         with:
-          ssh-key: ${{ secrets.DOCUMENTER_KEY }}
+          ssh-key: ${{ secrets.DOCUMENTER_KEY_NO_BASE64 }}
       - uses: julia-actions/setup-julia@v1
         with:
           version: '1' # Keep in sync with version that builds docs