Add SSH key to TagBot (#287)

This allows to trigger build of documentation when TagBot creates a new tag

Author: giordano

.github/workflows/TagBot.yml

@@ -12,3 +12,4 @@ jobs:
       - uses: JuliaRegistries/TagBot@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+          ssh: ${{ secrets.DOCUMENTER_KEY }}