Use SSH deployment key to bump version and tag release candiate (#6789)

To allow this workflow to run even though normal contributors
are required to create a pull request.

Steps:

1. Generate SSH key pair: ssh-keygen -t ed25519. No need for passphrases etc.
2. Add public key (.pub one) as a deploy key at Your repo -> Settings ->
   Security -> Deploy keys, check "Allow write access".
3. Add private key as a secret at Your repo -> Settings -> Security -> Secrets
   and variables -> Actions

https://stackoverflow.com/a/76135647/1809872

Co-authored-by: github-actions <github-actions@github.com>

.github/workflows/periodic-snapshot.yml

@@ -13,6 +13,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ssh-key: ${{secrets.ACTION_PUSH_KEY}}
       - run: |
           date="$(date +%y.%m).0-dev"
           gawk -i inplace -F: -v q=\" -v tag=$date '/^  "version": / { print $1 FS, q tag q ","; next} { print }' package.json